Can someone help me figure out what's wrong, please? I use MultiMC as my Minecraft launcher. I'm trying to get a new instance up and running. However, Minecraft crashes whenever I have OptiFabric (optifabric-1.9.6) and OptiFine (OptiFine_1.16.5_HD_U_G7) loaded. The instance runs fine without them.

Please let me know if the following crash report is not what you need.

---- Minecraft Crash Report ----
// You're mean.

Time: 2/28/21 6:16 AM
Description: Initializing game

java.lang.RuntimeException: Could not execute entrypoint stage 'client' due to errors, provided by 'imm_ptl_core'!
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:53)
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke(EntrypointUtils.java:36)
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointClient.start(EntrypointClient.java:33)
at net.minecraft.class_310.(class_310.java:437)
at net.minecraft.client.main.Main.main(Main.java:177)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:226)
at net.fabricmc.loader.launch.knot.Knot.launch(Knot.java:146)
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:28)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:196)
at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:231)
at org.multimc.EntryPoint.listen(EntryPoint.java:143)
at org.multimc.EntryPoint.main(EntryPoint.java:34)
Caused by: java.lang.NoClassDefFoundError: me/jellysquid/mods/sodium/client/SodiumHooks
at com.qouteall.hiding_in_the_bushes.sodium_compatibility.SodiumInterfaceInitializer.init(SodiumInterfaceInitializer.java:32)
at com.qouteall.hiding_in_the_bushes.ModEntryClient.onInitializeClient(ModEntryClient.java:71)
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:50)
... 19 more
Caused by: java.lang.ClassNotFoundException: me.jellysquid.mods.sodium.client.SodiumHooks
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:168)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 22 more

A detailed walkthrough of the error, its code path and all known details is as follows:

-- Head --
Thread: Render thread
Stacktrace:
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:53)
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke(EntrypointUtils.java:36)
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointClient.start(EntrypointClient.java:33)
at net.minecraft.class_310.(class_310.java:437)

-- Initialization --
Details:
Stacktrace:
at net.minecraft.client.main.Main.main(Main.java:177)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:226)
at net.fabricmc.loader.launch.knot.Knot.launch(Knot.java:146)
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:28)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:196)
at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:231)
at org.multimc.EntryPoint.listen(EntryPoint.java:143)
at org.multimc.EntryPoint.main(EntryPoint.java:34)

-- System Details --
Details:
Minecraft Version: 1.16.5
Minecraft Version ID: 1.16.5
Operating System: Windows 10 (amd64) version 10.0
Java Version: 1.8.0_281, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 7069649680 bytes (6742 MB) / 8410103808 bytes (8020 MB) up to 8410103808 bytes (8020 MB)
CPUs: 6
JVM Flags: 3 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xms8192m -Xmx8192m
Fabric Mods:
afktape: AFKTape 1.1.1
amecsapi: Amecs API 1.1.1+mc1.16-rc1
angerable-patch: Angerable Patch 1.1.0-1.16.4
appleskin: AppleSkin 1.0.11
architectury: Architectury 1.8.128
armor_hud: BerdinskiyBear's ArmorHUD 0.3.0
audiooutput: AudioOutput 0.0.3
autoconfig1u: Auto Config v1 Updated 3.3.1
better_end_skies: Better End Sky 1.1.0
better_mod_button: Better Mod Button 1.1.4
betterend: Better End 0.5.1-beta
betternether: Better Nether 5.0.5
blue_endless_jankson: jankson 1.2.0
cardinal-components-base: Cardinal Components API (base) 2.7.2
cardinal-components-entity: Cardinal Components API (entities) 2.7.2
cardinal-components-item: Cardinal Components API (items) 2.7.2
clickthrough: ClickThrough 1.16.4-fabric0.25.1-0.3
cloth-basic-math: Cloth Basic Math 0.5.1
cloth-client-events-v0: Cloth Client Events v0 1.5.47
cloth-config2: Cloth Config v4 4.11.14
coloredcraftingstations: ColoredCraftingStations 1.1.0
com_electronwill_night-config_core: core 3.6.0
com_electronwill_night-config_toml: toml 3.6.0
com_github_therandomlabs_trlutils-config: TRLUtils-Config master-SNAPSHOT
com_github_therandomlabs_trlutils-fabric: TRLUtils-Fabric 1.16-SNAPSHOT
cotton-client-commands: Cotton Client Commands 1.0.1+1.16-rc1
crowdin-translate: CrowdinTranslate 1.2
curios: Curios API 0.0.11-1.16.4
diggusmaximus: Diggus Maximus 1.4.2-1.16.3
dynamicsoundfilters: Dynamic Sound Filters 1.2.0+1.16.5
enchantedbookredesign: Enchanted Book Redesign 1.1
fabric: Fabric API 0.31.0+1.16
fabric-api-base: Fabric API Base 0.2.1+9354966b7d
fabric-biome-api-v1: Fabric Biome API (v1) 3.1.1+ca58154a7d
fabric-blockrenderlayer-v1: Fabric BlockRenderLayer Registration (v1) 1.1.5+ca58154a7d
fabric-command-api-v1: Fabric Command API (v1) 1.1.0+f9b3753b7d
fabric-commands-v0: Fabric Commands (v0) 0.2.2+ca58154a7d
fabric-containers-v0: Fabric Containers (v0) 0.1.11+9354966b7d
fabric-content-registries-v0: Fabric Content Registries (v0) 0.2.1+ca58154a7d
fabric-crash-report-info-v1: Fabric Crash Report Info (v1) 0.1.3+ca58154a7d
fabric-dimensions-v1: fabric-dimensions-v1 2.0.6+9354966b7d
fabric-entity-events-v1: Fabric Entity Events (v1) 1.0.3+ca58154a7d
fabric-events-interaction-v0: Fabric Events Interaction (v0) 0.4.2+ca58154a7d
fabric-events-lifecycle-v0: Fabric Events Lifecycle (v0) 0.2.1+ca58154a7d
fabric-game-rule-api-v1: Fabric Game Rule API (v1) 1.0.6+ca58154a7d
fabric-item-api-v1: Fabric Item API (v1) 1.2.1+ca58154a7d
fabric-item-groups-v0: Fabric Item Groups (v0) 0.2.3+ca58154a7d
fabric-key-binding-api-v1: Fabric Key Binding API (v1) 1.0.4+9354966b7d
fabric-keybindings-v0: Fabric Key Bindings (v0) 0.2.1+ca58154a7d
fabric-lifecycle-events-v1: Fabric Lifecycle Events (v1) 1.2.1+ca58154a7d
fabric-loot-tables-v1: Fabric Loot Tables (v1) 1.0.2+ca58154a7d
fabric-mining-levels-v0: Fabric Mining Levels (v0) 0.1.3+ca58154a7d
fabric-models-v0: Fabric Models (v0) 0.2.1+ca58154a7d
fabric-networking-api-v1: Fabric Networking API (v1) 1.0.1+ca58154a7d
fabric-networking-blockentity-v0: Fabric Networking Block Entity (v0) 0.2.8+ca58154a7d
fabric-networking-v0: Fabric Networking (v0) 0.3.2+ca58154a7d
fabric-object-builder-api-v1: Fabric Object Builder API (v1) 1.9.4+9354966b7d
fabric-object-builders-v0: Fabric Object Builders (v0) 0.7.2+ca58154a7d
fabric-particles-v1: Fabric Particles (v1) 0.2.4+ca58154a7d
fabric-registry-sync-v0: Fabric Registry Sync (v0) 0.7.4+ca58154a7d
fabric-renderer-api-v1: Fabric Renderer API (v1) 0.4.1+ca58154a7d
fabric-renderer-indigo: Fabric Renderer - Indigo 0.4.4+ca58154a7d
fabric-renderer-registries-v1: Fabric Renderer Registries (v1) 2.2.1+ca58154a7d
fabric-rendering-data-attachment-v1: Fabric Rendering Data Attachment (v1) 0.1.5+ca58154a7d
fabric-rendering-fluids-v1: Fabric Rendering Fluids (v1) 0.1.13+ca58154a7d
fabric-rendering-v0: Fabric Rendering (v0) 1.1.2+ca58154a7d
fabric-rendering-v1: Fabric Rendering (v1) 1.5.1+ca58154a7d
fabric-resource-loader-v0: Fabric Resource Loader (v0) 0.4.2+ca58154a7d
fabric-screen-api-v1: Fabric Screen API (v1) 1.0.0+c045166c7d
fabric-screen-handler-api-v1: Fabric Screen Handler API (v1) 1.1.5+9354966b7d
fabric-structure-api-v1: Fabric Structure API (v1) 1.1.4+ca58154a7d
fabric-tag-extensions-v0: Fabric Tag Extensions (v0) 1.1.1+ca58154a7d
fabric-textures-v0: Fabric Textures (v0) 1.0.6+ca58154a7d
fabric-tool-attribute-api-v1: Fabric Tool Attribute API (v1) 1.2.6+ca58154a7d
fabricloader: Fabric Loader 0.11.2
fallingleaves: Falling Leaves 1.5.0+1.16.5
gbfabrictools: GBfabrictools 1.3.2+1.16.4
grid: Grid 1.16.4-fabric0.25.1-1.6.4
imm_ptl_core: Immersive Portals Core 0.80
immersive_portals: Immersive Portals 0.80
java: Java HotSpot(TM) 64-Bit Server VM 8
kyrptconfig: Kytpt Config 1.1.4-1.16
leaf-decay: Leaf Decay 1.2.0-1.16.1
libcd: LibCapableData 3.0.3+1.16.3
lightoverlay: Light Overlay 5.8.0
lithium: Lithium 0.6.4
magna: Magna 1.4.2-1.16.2
minecraft: Minecraft 1.16.5
modmenu: Mod Menu 1.14.6+build.31
moreblocksmod: More Blocks Mod 0.1.3
mousewheelie: Mouse Wheelie 1.6.3+mc1.16.4
phosphor: Phosphor 0.7.1+build.11
repurposed_structures: Repurposed Structures 1.16.5-1.8.3
ring_of_attraction: Ring Of Attraction 1.0.29
rotten: FleshZ 1.2.2
roughlyenoughitems: Roughly Enough Items 5.10.184
roughlyenoughitems-api: REI (API) 5.10.184
roughlyenoughitems-default-plugin: REI (Default Plugin) 5.10.184
roughlyenoughitems-runtime: REI (Runtime) 5.10.184
roughlyenoughresources: Roughly Enough Resources 2.1.3
shuffle: Shuffle 1.2.0
silkspawners: SilkSpawners 1.0.0
sodium: Sodium 0.1.0
sodium-extra: Sodium Extra 0.2.0
static-content: Static Content 1.0.1-1.16.2
staticdata: Static Data 1.1.2
torohealth: ToroHealth Damage Indicators 1.16.4-fabric-4
tweed: Tweed API 3.0.0-beta.22
vanilla-hammers: Vanilla Hammers 3.0.1-1.16.3
vanilladeathchest: VanillaDeathChest 1.16.3-1.11.0.7-fabric
voyager: Voyager 1.0.0
waila: Hwyla 1.9.22
xaerominimap: Xaero's Minimap 21.4.1
xaeroworldmap: Xaero's World Map 1.12.1
Launched Version: MultiMC5
Backend library: LWJGL version 3.2.2 build 10
Backend API: NO CONTEXT
GL Caps:
Using VBOs: Yes
Is Modded: Definitely; Client brand changed to 'fabric'
Type: Client (map_client.txt)
CPU:

You can't use Sodium and OptiFabric at the same time. Would have thought it would have actually stopped the game from loading and told you though rather than letting it run anyway.

Looks like whatever compatibility issues Better End Sky 1.1 had with OptiFine they were apparently fixed in 1.2. Very odd where Sodium is getting loaded from all the same though given it doesn't look like it's including it.