My Fabric crashes when I try to open the ingame modifications list with 8 mods installed, the following error occurs:
crash-2020-12-11_11.57.06-client.txt

`---- Minecraft Crash Report ----
// Don't do that.

Time: 11.12.20 11:57
Description: Rendering screen

java.lang.IllegalAccessError: tried to access method net.minecraft.class_350.method_25331()I from class io.github.prospector.modmenu.gui.DescriptionListWidget
at io.github.prospector.modmenu.gui.DescriptionListWidget.renderScrollBar(DescriptionListWidget.java:106)
at io.github.prospector.modmenu.gui.DescriptionListWidget.method_25394(DescriptionListWidget.java:95)
at io.github.prospector.modmenu.gui.ModsScreen.method_25394(ModsScreen.java:253)
at net.minecraft.class_757.method_3192(class_757.java:616)
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:141)
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:27)

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

-- Head --
Thread: Render thread
Stacktrace:
at io.github.prospector.modmenu.gui.DescriptionListWidget.renderScrollBar(DescriptionListWidget.java:106)
at io.github.prospector.modmenu.gui.DescriptionListWidget.method_25394(DescriptionListWidget.java:95)
at io.github.prospector.modmenu.gui.ModsScreen.method_25394(ModsScreen.java:253)

-- Screen render details --
Details:
Screen name: io.github.prospector.modmenu.gui.ModsScreen
Mouse location: Scaled: (273, 227). Absolute: (547.000000, 455.000000)
Screen size: Scaled: (479, 509). Absolute: (958, 1018). Scale factor of 2.000000
Stacktrace:
at net.minecraft.class_757.method_3192(class_757.java:616)
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:141)
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:27)

-- 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: 1441078040 bytes (1374 MB) / 2785017856 bytes (2656 MB) up to 3221225472 bytes (3072 MB)
CPUs: 4
JVM Flags: 9 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xss1M -Xmx3G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
Fabric Mods:
fabric: Fabric API 0.26.3+1.16
fabric-api-base: Fabric API Base 0.2.0+ab87788d3a
fabric-biome-api-v1: Fabric Biome API (v1) 3.1.0+2e23b97c3a
fabric-blockrenderlayer-v1: Fabric BlockRenderLayer Registration (v1) 1.1.4+6a2618f53a
fabric-command-api-v1: Fabric Command API (v1) 1.0.9+6a2618f53a
fabric-commands-v0: Fabric Commands (v0) 0.2.0+6a2618f53a
fabric-containers-v0: Fabric Containers (v0) 0.1.8+6a2618f53a
fabric-content-registries-v0: Fabric Content Registries (v0) 0.1.9+6a2618f53a
fabric-crash-report-info-v1: Fabric Crash Report Info (v1) 0.1.2+b7f9825d3a
fabric-events-interaction-v0: Fabric Events Interaction (v0) 0.4.1+6a2618f53a
fabric-events-lifecycle-v0: Fabric Events Lifecycle (v0) 0.2.0+6a2618f53a
fabric-game-rule-api-v1: Fabric Game Rule API (v1) 1.0.3+a4467d2a3a
fabric-item-api-v1: Fabric Item API (v1) 1.2.0+6a2618f53a
fabric-item-groups-v0: Fabric Item Groups (v0) 0.2.1+6a2618f53a
fabric-key-binding-api-v1: Fabric Key Binding API (v1) 1.0.1+730711c63a
fabric-keybindings-v0: Fabric Key Bindings (v0) 0.2.0+3fa9f7c5fa
fabric-lifecycle-events-v1: Fabric Lifecycle Events (v1) 1.2.0+6a2618f53a
fabric-loot-tables-v1: Fabric Loot Tables (v1) 1.0.1+6a2618f53a
fabric-mining-levels-v0: Fabric Mining Levels (v0) 0.1.2+6a2618f53a
fabric-models-v0: Fabric Models (v0) 0.1.1+6a2618f53a
fabric-networking-blockentity-v0: Fabric Networking Block Entity (v0) 0.2.5+6a2618f53a
fabric-networking-v0: Fabric Networking (v0) 0.1.10+6a2618f53a
fabric-object-builder-api-v1: Fabric Object Builder API (v1) 1.9.2+6a2618f53a
fabric-object-builders-v0: Fabric Object Builders (v0) 0.7.1+6a2618f53a
fabric-particles-v1: fabric-particles-v1 0.2.2+6a2618f53a
fabric-registry-sync-v0: Fabric Registry Sync (v0) 0.7.1+285766753a
fabric-renderer-api-v1: Fabric Renderer API (v1) 0.3.3+6a2618f53a
fabric-renderer-indigo: Fabric Renderer - Indigo 0.4.3+6a2618f53a
fabric-renderer-registries-v1: Fabric Renderer Registries (v1) 2.2.0+6a2618f53a
fabric-rendering-data-attachment-v1: Fabric Rendering Data Attachment (v1) 0.1.4+6a2618f53a
fabric-rendering-fluids-v1: Fabric Rendering Fluids (v1) 0.1.12+6a2618f53a
fabric-rendering-v0: Fabric Rendering (v0) 1.1.1+6a2618f53a
fabric-rendering-v1: Fabric Rendering (v1) 1.4.0+6a2618f53a
fabric-resource-loader-v0: Fabric Resource Loader (v0) 0.3.2+1944f3e03a
fabric-screen-handler-api-v1: Fabric Screen Handler API (v1) 1.1.0+6a2618f53a
fabric-structure-api-v1: Fabric Structure API (v1) 1.1.1+f1d8af063a
fabric-tag-extensions-v0: Fabric Tag Extensions (v0) 1.0.3+6a2618f53a
fabric-textures-v0: Fabric Textures (v0) 1.0.5+6a2618f53a
fabric-tool-attribute-api-v1: Fabric Tool Attribute API (v1) 1.2.5+6a2618f53a
fabricloader: Fabric Loader 0.10.8
lambdynlights: LambDynamicLights 1.3.2+1.16.4
lithium: Lithium 0.6.0
lithium-api: Lithium API 0.6.0
logical_zoom: Logical Zoom 0.0.7
minecraft: Minecraft 1.16.3
modmenu: Mod Menu 1.14.13+build.19
phosphor: Phosphor 0.6.0+build.7
replaymod: Replay Mod 1.16.3-2.4.5
sodium: Sodium 0.1.0
spruceui: SpruceUI 1.6.4
waila: Hwyla 1.9.22
Launched Version: fabric-loader-0.10.8-1.16.3
Backend library: LWJGL version 3.2.2 build 10
Backend API: GeForce GTX 750 Ti/PCIe/SSE2 GL version 4.6.0 NVIDIA 432.00, 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: fabric/logical_zoom, fabric/fabric-renderer-api-v1, fabric/fabric-keybindings-v0, fabric/fabricloader, fabric/fabric-containers-v0, fabric/lithium, fabric/fabric-object-builder-api-v1, fabric/fabric-game-rule-api-v1, fabric/fabric-api-base, fabric/fabric-rendering-data-attachment-v1, fabric/lambdynlights, fabric/fabric-textures-v0, fabric/fabric-rendering-fluids-v1, fabric/waila, fabric/fabric-blockrenderlayer-v1, fabric/fabric-lifecycle-events-v1, fabric/sodium, fabric/fabric-renderer-registries-v1, fabric/fabric-loot-tables-v1, fabric/fabric, fabric/fabric-networking-v0, fabric/fabric-networking-blockentity-v0, fabric/fabric-screen-handler-api-v1, fabric/modmenu, fabric/fabric-command-api-v1, fabric/phosphor, fabric/fabric-tool-attribute-api-v1, fabric/fabric-renderer-indigo, fabric/fabric-crash-report-info-v1, fabric/fabric-events-interaction-v0, fabric/fabric-item-api-v1, fabric/fabric-rendering-v0, fabric/fabric-key-binding-api-v1, fabric/fabric-rendering-v1, fabric/spruceui, fabric/fabric-resource-loader-v0, fabric/fabric-content-registries-v0, fabric/fabric-tag-extensions-v0, fabric/fabric-biome-api-v1, fabric/fabric-registry-sync-v0, fabric/fabric-mining-levels-v0, fabric/fabric-events-lifecycle-v0, fabric/fabric-models-v0, fabric/fabric-item-groups-v0, fabric/fabric-object-builders-v0
Current Language: Deutsch (Deutschland)
CPU: 4x Intel(R) Core(TM) i5-4460 CPU @ 3.20GHz`

The mods list is not part of Fabric. It is part of ModMenu.
You're running Minecraft 1.16.3, but the ModMenu version you're using is for 1.16.4. Usually mods work across patch versions of MC, but AFAIK 1.16.x is an exception. Also this looks like the kind of error a mismatch would cause.
Try updating Minecraft, Fabric, and all of your mods to 1.16.4; or try a version of ModMenu for 1.16.1.

Closing since modmenu is not part of fabric api. See above message for solution.