I've tried with both the _MOD.jar and the main file, neither of them works.

[09:34:45] [main/INFO]: Loading for game Minecraft 1.16.5
[09:34:45] [ForkJoinPool-1-worker-13/WARN]: Non-Fabric mod JAR at "C:\Users<my name>\AppData\Roaming.minecraft\immersive\mods\OptiFine_1.16.5_HD_U_G8_MOD.jar", ignoring
[09:34:46] [main/INFO]: [FabricLoader] Loading 55 mods:
- [email protected]
- [email protected]
- [email protected]+1.16
- [email protected]+c88702897d
- [email protected]+731c05f37d
- [email protected]+3661eaa17d
- [email protected]+ca58154a7d
- [email protected]+351679a77d
- [email protected]+ca58154a7d
- [email protected]+9354966b7d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+61336ba97d
- [email protected]+c88702897d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+2868a2287d
- [email protected]+9354966b7d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+bc7a746f7d
- [email protected]+e3c9d0627d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+c88702897d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+0ef801b67d
- [email protected]+ca58154a7d
- [email protected]+2868a2287d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+2868a2287d
- [email protected]+2868a2287d
- [email protected]+c045166c7d
- [email protected]+9354966b7d
- [email protected]+ca0ef93d7d
- [email protected]+ca58154a7d
- [email protected]+ca58154a7d
- [email protected]+8183d3957d
- [email protected]
- [email protected]
- [email protected]
- java@8
- [email protected]
- [email protected]
- [email protected]+unknown.bd9230a
- [email protected]
- [email protected]+1.14.4-1.17
[09:34:46] [main/WARN]: Mod modmenu (v1.16.8+unknown.bd9230a) does not respect SemVer - comparison support is limited.
[09:34:46] [main/INFO]: SpongePowered MIXIN Subsystem Version=0.8.2 Source=file:/C:/Users/calvi/AppData/Roaming/.minecraft/libraries/net/fabricmc/sponge-mixin/0.9.4+mixin.0.8.2/sponge-mixin-0.9.4+mixin.0.8.2.jar Service=Knot/Fabric Env=CLIENT
[09:34:47] [main/WARN]: @mixin target net/minecraft/class_3898$class_3208 is public in fabric-networking-api-v1.mixins.json:accessor.EntityTrackerAccessor and should be specified in value
[09:34:47] [main/WARN]: @mixin target net/minecraft/class_3898$class_3208 is public in imm_ptl.mixins.json:common.entity_sync.MixinEntityTracker and should be specified in value
[09:34:47] [main/WARN]: Error loading class: org/jetbrains/annotations/ApiStatus$ScheduledForRemoval (java.lang.ClassNotFoundException: org/jetbrains/annotations/ApiStatus$ScheduledForRemoval)
[09:35:01] [main/INFO]: [OptiFine] (Reflector) Field not found: World.tileEntitiesToBeRemoved
[09:35:03] [main/INFO]: [OptiFine] (Reflector) Method not present: net.minecraft.class_3489.createOptional
[09:35:07] [main/INFO]: Environment: authHost='https://authserver.mojang.com', accountsHost='https://api.mojang.com', sessionHost='https://sessionserver.mojang.com', servicesHost='https://api.minecraftservices.com', name='PROD'
[09:35:09] [main/INFO]: Setting user: the_zombie_dude
[09:35:09] [main/INFO]: Definitely not up to no good
[09:35:09] [main/INFO]: Immersive Portals Mod Initializing
[09:35:09] [main/INFO]: Reach entity attributes mod is not present
[09:35:09] [main/INFO]: Pehkui is present
[09:35:10] [main/INFO]: IP Config Applied
[09:35:10] [main/INFO]: Optifine is present
[09:35:10] [main/INFO]: Sodium is not present
[09:35:10] [main/WARN]: WARNING! Mod mm is only using deprecated 'modmenu:api' custom value! This will be removed in 1.18 snapshots, so ask the author of this mod to support the new API.
[09:35:10] [main/WARN]: WARNING! Mod cloth-basic-math is only using deprecated 'modmenu:api' custom value! This will be removed in 1.18 snapshots, so ask the author of this mod to support the new API.
[09:35:10] [main/WARN]: WARNING! Mod cloth-config2 is only using deprecated 'modmenu:api' custom value! This will be removed in 1.18 snapshots, so ask the author of this mod to support the new API.
[09:35:10] [main/INFO]: [Indigo] Registering Indigo renderer!
[09:35:10] [main/INFO]: [Indigo] Compatibility mode enabled.
[09:35:11] [main/INFO]: Backend library: LWJGL version 3.2.2 build 10
[09:35:13] [main/INFO]: [OptiFine]
[09:35:13] [main/INFO]: [OptiFine] OptiFine_1.16.5_HD_U_G8
[09:35:13] [main/INFO]: [OptiFine] Build: 20210515-161946
[09:35:13] [main/INFO]: [OptiFine] OS: Windows 10 (amd64) version 10.0
[09:35:13] [main/INFO]: [OptiFine] Java: 1.8.0_51, Oracle Corporation
[09:35:13] [main/INFO]: [OptiFine] VM: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
[09:35:13] [main/INFO]: [OptiFine] LWJGL: 3.3.0 Win32 WGL EGL OSMesa VisualC DLL
[09:35:13] [main/INFO]: [OptiFine] OpenGL: NVIDIA GeForce RTX 2060/PCIe/SSE2, version 4.6.0 NVIDIA 466.47, NVIDIA Corporation
[09:35:13] [main/INFO]: [OptiFine] OpenGL Version: 4.6.0
[09:35:13] [main/INFO]: [OptiFine] Maximum texture size: 32768x32768
[09:35:13] [VersionCheck/INFO]: [OptiFine] Checking for new version
[09:35:13] [main/FATAL]: Mixin apply failed imm_ptl_optifine.mixins.json:MixinShaders_Swap -> net.optifine.shaders.Shaders: org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException @shadow field colorBufferSizes was not located in the target class net.optifine.shaders.Shaders. Using refmap imm_ptl_core-refmap.json
org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException: @shadow field colorBufferSizes was not located in the target class net.optifine.shaders.Shaders. Using refmap imm_ptl_core-refmap.json
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attachFields(MixinPreProcessorStandard.java:610) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attach(MixinPreProcessorStandard.java:289) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.createContextFor(MixinPreProcessorStandard.java:264) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinInfo.createContextFor(MixinInfo.java:1272) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:287) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:345) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:569) [sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:351) [sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:208) [sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:178) [sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.FabricMixinTransformerProxy.transformClassBytes(FabricMixinTransformerProxy.java:23) [fabric-loader-0.11.6.jar:0.9.4+mixin.0.8.2]
at net.fabricmc.loader.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:162) [fabric-loader-0.11.6.jar:?]
at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:154) [fabric-loader-0.11.6.jar:?]
at java.lang.ClassLoader.loadClass(ClassLoader.java:357) [?:1.8.0_51]
at net.optifine.Config.initDisplay(Config.java:221) [Optifine-mapped.jar:?]
at net.minecraft.class_4493.method_21973(class_4493.java:429) [intermediary-fabric-loader-0.11.6-1.16.5.jar:?]
at com.mojang.blaze3d.platform.GLX._init(GLX.java:151) [intermediary-fabric-loader-0.11.6-1.16.5.jar:?]
at com.mojang.blaze3d.systems.RenderSystem.initRenderer(RenderSystem.java:1065) [intermediary-fabric-loader-0.11.6-1.16.5.jar:?]
at net.minecraft.class_310.(class_310.java:478) [intermediary-fabric-loader-0.11.6-1.16.5.jar:?]
at net.minecraft.client.main.Main.main(Main.java:177) [intermediary-fabric-loader-0.11.6-1.16.5.jar:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_51]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_51]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_51]
at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_51]
at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:234) [fabric-loader-0.11.6.jar:?]
at net.fabricmc.loader.launch.knot.Knot.launch(Knot.java:153) [fabric-loader-0.11.6.jar:?]
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:28) [fabric-loader-0.11.6.jar:?]
[09:35:13] [main/FATAL]: Mixin apply failed imm_ptl_optifine.mixins.json:MixinShaders_Swap -> net.optifine.shaders.Shaders: org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException @shadow field colorBufferSizes was not located in the target class net.optifine.shaders.Shaders. Using refmap imm_ptl_core-refmap.json
org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException: @shadow field colorBufferSizes was not located in the target class net.optifine.shaders.Shaders. Using refmap imm_ptl_core-refmap.json
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attachFields(MixinPreProcessorStandard.java:610) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attach(MixinPreProcessorStandard.java:289) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.createContextFor(MixinPreProcessorStandard.java:264) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinInfo.createContextFor(MixinInfo.java:1272) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:287) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:345) ~[sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:569) [sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:351) [sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:208) [sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:178) [sponge-mixin-0.9.4+mixin.0.8.2.jar:0.9.4+mixin.0.8.2]
at org.spongepowered.asm.mixin.transformer.FabricMixinTransformerProxy.transformClassBytes(FabricMixinTransformerProxy.java:23) [fabric-loader-0.11.6.jar:0.9.4+mixin.0.8.2]
at net.fabricmc.loader.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:162) [fabric-loader-0.11.6.jar:?]
at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:154) [fabric-loader-0.11.6.jar:?]
at java.lang.ClassLoader.loadClass(ClassLoader.java:357) [?:1.8.0_51]
at net.optifine.CrashReporter.extendCrashReport(CrashReporter.java:126) [Optifine-mapped.jar:?]
at net.optifine.CrashReporter.onCrashReport(CrashReporter.java:38) [Optifine-mapped.jar:?]
at net.minecraft.class_128.method_568(class_128.java:227) [intermediary-fabric-loader-0.11.6-1.16.5.jar:?]
at net.minecraft.class_310.method_1565(class_310.java:785) [intermediary-fabric-loader-0.11.6-1.16.5.jar:?]
at net.minecraft.client.main.Main.main(Main.java:186) [intermediary-fabric-loader-0.11.6-1.16.5.jar:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_51]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_51]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_51]
at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_51]
at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:234) [fabric-loader-0.11.6.jar:?]
at net.fabricmc.loader.launch.knot.Knot.launch(Knot.java:153) [fabric-loader-0.11.6.jar:?]
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:28) [fabric-loader-0.11.6.jar:?]
[09:35:13] [main/INFO]: [STDERR]: java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
[09:35:13] [main/INFO]: [STDERR]: at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:236)
[09:35:13] [main/INFO]: [STDERR]: at net.fabricmc.loader.launch.knot.Knot.launch(Knot.java:153)
[09:35:13] [main/INFO]: [STDERR]: at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:28)
[09:35:13] [main/INFO]: [STDERR]: Caused by: java.lang.reflect.InvocationTargetException
[09:35:13] [main/INFO]: [STDERR]: at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[09:35:13] [main/INFO]: [STDERR]: at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[09:35:13] [main/INFO]: [STDERR]: at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[09:35:13] [main/INFO]: [STDERR]: at java.lang.reflect.Method.invoke(Method.java:497)
[09:35:13] [main/INFO]: [STDERR]: at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:234)
[09:35:13] [main/INFO]: [STDERR]: ... 2 more
[09:35:13] [main/INFO]: [STDERR]: Caused by: org.spongepowered.asm.mixin.transformer.throwables.MixinTransformerError: An unexpected critical error was encountered
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:363)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:208)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:178)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.FabricMixinTransformerProxy.transformClassBytes(FabricMixinTransformerProxy.java:23)
[09:35:13] [main/INFO]: [STDERR]: at net.fabricmc.loader.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:162)
[09:35:13] [main/INFO]: [STDERR]: at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:154)
[09:35:13] [main/INFO]: [STDERR]: at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
[09:35:13] [main/INFO]: [STDERR]: at net.optifine.CrashReporter.extendCrashReport(CrashReporter.java:126)
[09:35:13] [main/INFO]: [STDERR]: at net.optifine.CrashReporter.onCrashReport(CrashReporter.java:38)
[09:35:13] [main/INFO]: [STDERR]: at net.minecraft.class_128.method_568(class_128.java:227)
[09:35:13] [main/INFO]: [STDERR]: at net.minecraft.class_310.method_1565(class_310.java:785)
[09:35:13] [main/INFO]: [STDERR]: at net.minecraft.client.main.Main.main(Main.java:186)
[09:35:13] [main/INFO]: [STDERR]: ... 7 more
[09:35:13] [main/INFO]: [STDERR]: Caused by: org.spongepowered.asm.mixin.throwables.MixinApplyError: Mixin [imm_ptl_optifine.mixins.json:MixinShaders_Swap] from phase [DEFAULT] in config [imm_ptl_optifine.mixins.json] FAILED during APPLY
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinProcessor.handleMixinError(MixinProcessor.java:642)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinProcessor.handleMixinApplyError(MixinProcessor.java:594)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:356)
[09:35:13] [main/INFO]: [STDERR]: ... 18 more
[09:35:13] [main/INFO]: [STDERR]: Caused by: org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException: @shadow field colorBufferSizes was not located in the target class net.optifine.shaders.Shaders. Using refmap imm_ptl_core-refmap.json
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attachFields(MixinPreProcessorStandard.java:610)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attach(MixinPreProcessorStandard.java:289)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.createContextFor(MixinPreProcessorStandard.java:264)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinInfo.createContextFor(MixinInfo.java:1272)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:287)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:345)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:569)
[09:35:13] [main/INFO]: [STDERR]: at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:351)
[09:35:13] [main/INFO]: [STDERR]: ... 18 more
[09:35:13] [VersionCheck/INFO]: [OptiFine] Version found: G7

This is an issue with Immersive Portals and OptiFine G8 (iPortalTeam/ImmersivePortalsMod#722), in the meantime I think it should be fine using G7.