I don't know what specifically the problem is but it only crashes once both OptiForge and Optifine is loaded. I'll post the crash report and hop something can be figured out here

---- Minecraft Crash Report ----
// Why did you do that?

Time: 10/29/20 4:19 PM
Description: Unexpected error

java.lang.NullPointerException: Unexpected error
at net.minecraft.class_761.method_3251(class_761.java:2208)
at net.minecraft.class_761.method_22710(class_761.java:1597)
at net.minecraft.class_757.method_3188(class_757.java:1022)
at net.minecraft.class_757.redirect$zko000$redirectRenderingWorld(class_757.java:2047)
at net.minecraft.class_757.method_3192(class_757.java:693)
at net.minecraft.class_310.method_1523(class_310.java:1023)
at net.minecraft.class_310.method_1514(class_310.java:656)
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:224)
at net.fabricmc.loader.launch.knot.Knot.init(Knot.java:140)
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:26)

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

-- Head --
Thread: Render thread
Stacktrace:
at net.minecraft.class_761.method_3251(class_761.java:2208)
at net.minecraft.class_761.method_22710(class_761.java:1597)
at net.minecraft.class_757.method_3188(class_757.java:1022)
at net.minecraft.class_757.redirect$zko000$redirectRenderingWorld(class_757.java:2047)

-- OptiFabric --
Details:
OptiFine jar designed for: 1.16.3
OptiFine jar version: OptiFine_1.16.3_HD_U_G3
OptiFine jar status: Valid OptiFine installer
OptiFine remapped jar: C:\Users\spide\AppData\Roaming.minecraft.optifine\OptiFine_1.16.3_HD_U_G3\Optifine-mapped.jar
OptiFabric error:
Stacktrace:
at net.minecraft.class_128.handler$zfg000$fillSystemDetails(class_128.java:523)
at net.minecraft.class_128.(class_128.java:55)
at net.minecraft.class_310.method_1514(class_310.java:679)
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:224)
at net.fabricmc.loader.launch.knot.Knot.init(Knot.java:140)
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:26)

-- Affected level --
Details:
All players: 1 total; [class_746['TheEkion'/227, l='ClientWorld minecraft:overworld', x=0.44, y=71.37, z=23.47]]
Chunk stats: Client Chunks (ImmPtl) 342
Level dimension: minecraft:overworld
Level spawn location: World: (0,62,2), Chunk: (at 0,3,2 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: 195 game time, 195 day time
Server brand: fabric
Server type: Integrated singleplayer server

-- System Details --
Details:
Minecraft Version: 1.16.3
Minecraft Version ID: 1.16.3
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: 1341676608 bytes (1279 MB) / 2147483648 bytes (2048 MB) up to 2147483648 bytes (2048 MB)
CPUs: 8
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:
appleskin: AppleSkin 1.0.11
autoconfig1u: Auto Config v1 Updated 3.2.2
cloth-basic-math: Cloth Basic Math 0.5.1
cloth-config2: Cloth Config v4 4.8.2
durabilityviewer: Giselbaers Durability Viewer 1.16.2-fabric0.17.2-1.8.7
fabric: Fabric API 0.24.3+build.414-1.16
fabric-api-base: Fabric API Base 0.2.0+9f0fb4b895
fabric-biome-api-v1: Fabric Biome API (v1) 2.0.0+c29459ab95
fabric-blockrenderlayer-v1: Fabric BlockRenderLayer Registration (v1) 1.1.4+c6a8ea8995
fabric-containers-v0: Fabric Containers (v0) 0.1.8+045df74f95
fabric-content-registries-v0: Fabric Content Registries (v0) 0.1.9+059ea86695
fabric-crash-report-info-v1: Fabric Crash Report Info (v1) 0.1.2+b7f9825d95
fabric-events-interaction-v0: Fabric Events Interaction (v0) 0.4.1+f8ac1db295
fabric-events-lifecycle-v0: Fabric Events Lifecycle (v0) 0.2.0+16acbe5b95
fabric-game-rule-api-v1: Fabric Game Rule API (v1) 1.0.3+a4467d2a95
fabric-item-api-v1: Fabric Item API (v1) 1.2.0+f8ac1db295
fabric-item-groups-v0: Fabric Item Groups (v0) 0.2.1+a4467d2a95
fabric-key-binding-api-v1: Fabric Key Binding API (v1) 1.0.1+730711c695
fabric-keybindings-v0: Fabric Key Bindings (v0) 0.2.0+3fa9f7c595
fabric-lifecycle-events-v1: Fabric Lifecycle Events (v1) 1.2.0+74cc3b2095
fabric-loot-tables-v1: Fabric Loot Tables (v1) 1.0.1+432ea18895
fabric-mining-levels-v0: Fabric Mining Levels (v0) 0.1.2+b764ce9995
fabric-models-v0: Fabric Models (v0) 0.1.1+f8ac1db295
fabric-networking-blockentity-v0: Fabric Networking Block Entity (v0) 0.2.5+b50ffc7b95
fabric-networking-v0: Fabric Networking (v0) 0.1.10+e00ecb5f95
fabric-object-builder-api-v1: Fabric Object Builder API (v1) 1.9.2+a89534ab95
fabric-object-builders-v0: Fabric Object Builders (v0) 0.7.1+a4467d2a95
fabric-particles-v1: fabric-particles-v1 0.2.2+fb0d9b0e95
fabric-registry-sync-v0: Fabric Registry Sync (v0) 0.6.1+a4467d2a95
fabric-renderer-api-v1: Fabric Renderer API (v1) 0.3.3+a4467d2a95
fabric-renderer-indigo: Fabric Renderer - Indigo 0.4.3+a4467d2a95
fabric-renderer-registries-v1: Fabric Renderer Registries (v1) 2.2.0+f8ac1db295
fabric-rendering-data-attachment-v1: Fabric Rendering Data Attachment (v1) 0.1.4+f8ac1db295
fabric-rendering-fluids-v1: Fabric Rendering Fluids (v1) 0.1.12+f8ac1db295
fabric-rendering-v0: Fabric Rendering (v0) 1.1.1+f8ac1db295
fabric-rendering-v1: Fabric Rendering (v1) 1.3.1+f8ac1db295
fabric-resource-loader-v0: Fabric Resource Loader (v0) 0.3.1+facf3bbf95
fabric-screen-handler-api-v1: Fabric Screen Handler API (v1) 1.1.0+8724984195
fabric-structure-api-v1: Fabric Structure API (v1) 1.1.0+f8ac1db295
fabric-tag-extensions-v0: Fabric Tag Extensions (v0) 1.0.3+ac8e8c5995
fabric-textures-v0: Fabric Textures (v0) 1.0.5+a4467d2a95
fabric-tool-attribute-api-v1: Fabric Tool Attribute API (v1) 1.2.4+2b46237995
fabricloader: Fabric Loader 0.10.3+build.211
gbfabrictools: GBfabrictools 1.2.3+1.16.2
gravestones: Gravestones 1.5
illuminations: Illuminations 1.2.2
imm_ptl_core: Immersive Portals Core 0.41
immersive_portals: Immersive Portals 0.41
minecraft: Minecraft 1.16.3
mm: Manningham Mills 2.1
modmenu: Mod Menu 1.14.6+build.31
optifabric: OptiFabric 1.7.0
torohealth: ToroHealth Damage Indicators 1.16.3-fabric-1
xaerominimap: Xaero's Minimap 20.26.0
Launched Version: fabric-loader-0.10.3+build.211-1.16.3
Backend library: LWJGL version 3.2.2 build 10
Backend API: GeForce GTX 950/PCIe/SSE2 GL version 4.6.0 NVIDIA 456.55, 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: fancy
Resource Packs: vanilla, file/Faithful-1.16.3.zip
Current Language: English (US)
CPU: 8x Intel(R) Core(TM) i7-4770K CPU @ 3.50GHz
OptiFine Version: OptiFine_1.16.3_HD_U_G3
OptiFine Build: 20200916-082411
Render Distance Chunks: 9
Mipmaps: 0
Anisotropic Filtering: 1
Antialiasing: 0
Multitexture: false
Shaders: null
OpenGlVersion: 4.6.0 NVIDIA 456.55
OpenGlRenderer: GeForce GTX 950/PCIe/SSE2
OpenGlVendor: NVIDIA Corporation
CpuCount: 8

This can be avoided turning off render regions (as per iPortalTeam/ImmersivePortalsMod#433). Possibly is something that OptiFabric could work around without needing to universally turn it off though.

same, I can't even click the options button!