So I'm using the Fabric version of both mods for 1.16.5, I'm quite new to bug reporting however I do know you might want the crash report so I'll post it down below

The game runs perfectly but as soon as I light a portal and the chunks start loading it freezes for a moment and after that the game outright crashes
The mod doesn't seem to work with optifabric (and thus optifine) either, but instead of the game loading it just crashes without a crash report at all

---- Minecraft Crash Report ----
// Oh - I know what I did wrong!

Time: 2/20/21 12:02 PM
Description: Unexpected error

java.lang.NoClassDefFoundError: me/jellysquid/mods/sodium/client/IWorldRenderer
at com.qouteall.hiding_in_the_bushes.sodium_compatibility.SodiumInterfaceInitializer.lambda$init$0(SodiumInterfaceInitializer.java:18)
at com.qouteall.hiding_in_the_bushes.sodium_compatibility.SodiumInterfaceInitializer$$Lambda$2580/526417334.apply(Unknown Source)
at com.qouteall.immersive_portals.render.MyGameRenderer.switchAndRenderTheWorld(MyGameRenderer.java:179)
at com.qouteall.immersive_portals.render.MyGameRenderer.renderWorldNew(MyGameRenderer.java:75)
at com.qouteall.immersive_portals.render.PortalRenderer.invokeWorldRendering(PortalRenderer.java:223)
at com.qouteall.immersive_portals.render.PortalRenderer.renderPortalContent(PortalRenderer.java:188)
at com.qouteall.immersive_portals.render.RendererUsingStencil.doRenderPortal(RendererUsingStencil.java:140)
at com.qouteall.immersive_portals.render.PortalRenderer.renderPortals(PortalRenderer.java:110)
at com.qouteall.immersive_portals.render.RendererUsingStencil.doPortalRendering(RendererUsingStencil.java:53)
at com.qouteall.immersive_portals.render.RendererUsingStencil.onBeforeTranslucentRendering(RendererUsingStencil.java:48)
at net.minecraft.class_761.handler$zlm000$onBeforeTranslucentRendering(class_761.java:7724)
at net.minecraft.class_761.method_22710(class_761.java:1360)
at net.minecraft.class_757.method_3188(class_757.java:727)
at net.minecraft.class_757.redirect$zli000$redirectRenderingWorld(class_757.java:2051)
at net.minecraft.class_757.method_3192(class_757.java:546)
at net.minecraft.class_310.method_1523(class_310.java:1048)
at net.minecraft.class_310.method_1514(class_310.java:681)
at net.minecraft.client.main.Main.main(Main.java:215)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:226)
at net.fabricmc.loader.launch.knot.Knot.init(Knot.java:139)
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:27)
Caused by: java.lang.ClassNotFoundException: me.jellysquid.mods.sodium.client.IWorldRenderer
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:168)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 25 more

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

-- Head --
Thread: Render thread
Stacktrace:
at com.qouteall.hiding_in_the_bushes.sodium_compatibility.SodiumInterfaceInitializer.lambda$init$0(SodiumInterfaceInitializer.java:18)
at com.qouteall.hiding_in_the_bushes.sodium_compatibility.SodiumInterfaceInitializer$$Lambda$2580/526417334.apply(Unknown Source)
at com.qouteall.immersive_portals.render.MyGameRenderer.switchAndRenderTheWorld(MyGameRenderer.java:179)
at com.qouteall.immersive_portals.render.MyGameRenderer.renderWorldNew(MyGameRenderer.java:75)
at com.qouteall.immersive_portals.render.PortalRenderer.invokeWorldRendering(PortalRenderer.java:223)
at com.qouteall.immersive_portals.render.PortalRenderer.renderPortalContent(PortalRenderer.java:188)
at com.qouteall.immersive_portals.render.RendererUsingStencil.doRenderPortal(RendererUsingStencil.java:140)
at com.qouteall.immersive_portals.render.PortalRenderer.renderPortals(PortalRenderer.java:110)
at com.qouteall.immersive_portals.render.RendererUsingStencil.doPortalRendering(RendererUsingStencil.java:53)
at com.qouteall.immersive_portals.render.RendererUsingStencil.onBeforeTranslucentRendering(RendererUsingStencil.java:48)
at net.minecraft.class_761.handler$zlm000$onBeforeTranslucentRendering(class_761.java:7724)
at net.minecraft.class_761.method_22710(class_761.java:1360)
at net.minecraft.class_757.method_3188(class_757.java:727)
at net.minecraft.class_757.redirect$zli000$redirectRenderingWorld(class_757.java:2051)

-- Affected level --
Details:
All players: 0 total; []
Chunk stats: Client Chunks (ImmPtl) 0
Level dimension: minecraft:the_nether
Level spawn location: World: (8,64,8), Chunk: (at 8,4,8 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 1 game time, 1 day time
Server brand: fabric
Server type: Integrated singleplayer server
Stacktrace:
at net.minecraft.class_638.method_8538(class_638.java:449)
at net.minecraft.class_310.method_1587(class_310.java:2239)
at net.minecraft.class_310.method_1514(class_310.java:704)
at net.minecraft.client.main.Main.main(Main.java:215)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:226)
at net.fabricmc.loader.launch.knot.Knot.init(Knot.java:139)
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:27)

-- 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_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 547816848 bytes (522 MB) / 2013265920 bytes (1920 MB) up to 2147483648 bytes (2048 MB)
CPUs: 4
JVM Flags: 9 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xss1M -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
Fabric Mods:
cloth-basic-math: Cloth Basic Math 0.5.1
cloth-config2: Cloth Config v4 4.8.2
fabric: Fabric API 0.30.3+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) 1.0.10+ca58154a7d
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 0.11.1
imm_ptl_core: Immersive Portals Core 0.68
immersive_portals: Immersive Portals 0.68
java: Java HotSpot(TM) 64-Bit Server VM 8
minecraft: Minecraft 1.16.5
modmenu: Mod Menu 1.14.6+build.31
sodium: Sodium 0.1.1
Launched Version: fabric-loader-0.11.1-1.16.5
Backend library: LWJGL version 3.2.2 build 10
Backend API: GeForce GTX 970/PCIe/SSE2 GL version 4.6.0 NVIDIA 461.40, NVIDIA Corporation
GL Caps: Using framebuffer using OpenGL 3.0
Using VBOs: Yes
Is Modded: Definitely; Client brand changed to 'fabric'
Type: Client (map_client.txt)
Graphics mode: fast
Resource Packs: vanilla
Current Language: English (US)
CPU: 4x Intel(R) Core(TM) i5-7400 CPU @ 3.00GHz

So I'm using the Fabric version of both mods for 1.16.5, I'm quite new to bug reporting however I do know you might want the crash report so I'll post it down below

The game runs perfectly but as soon as I light a portal and the chunks start loading it freezes for a moment and after that the game outright crashes
The mod doesn't seem to work with optifabric (and thus optifine) either, but instead of the game loading it just crashes without a crash report at all

imm_ptl_core: Immersive Portals Core 0.68
immersive_portals: Immersive Portals 0.68
java: Java HotSpot(TM) 64-Bit Server VM 8
minecraft: Minecraft 1.16.5
modmenu: Mod Menu 1.14.6+build.31
sodium: Sodium 0.1.1

You are using Immersive Portals 0.68, and the fork of 0.1.1. You either need to upgrade Immersive Portals, or you need to downgrade your Sodium fork version. The first option is more recommended.

For Optifine compatibility, you need to upgrade Immersive Portals to a newer version.