ver: PureSuffering-1.21.1-1.6.6.0B NEOFORGE
Neoforge 21.1.73
Mods:
PureSuffering-1.21.1-1.6.6.0B
forgified-fabric-api-0.104.0+2.0.13+1.21.1

debug.log

Have you tried to test with neo forge version 21.1.74 along with forgified fabric version API 0.104.0+2.0.18+1.21.1?
You are using forgified fabric version "0.104.0+2.0.13+1.21.1" which maybe an outdated version. Pure-suffering 1.6.6.0B seems to work on my end.

video of it working: https://youtu.be/W36xIttYyng

This is quite an interesting bug since Its difficult to figure out who's at fault here. I can attempt to make my code work differently to avoid the problem, however I do believe the error "[31окт.2024 19:19:31.717] [main/WARN] [mixin/]: Error loading class: net/minecraft/client/multiplayer/ClientLevel (java.lang.RuntimeException: Attempted to load class net/minecraft/client/multiplayer/ClientLevel for invalid dist DEDICATED_SERVER)" that is shown right before the crash would imply that ForgifiedFabric is breaking some NeoForge mods so that Fabric mods can load properly. No promises I can provide a work around, but I'll give my best effort before I ask the other mod creator.

Problem only with server. Single world working fine

Thanks for letting us know, I'll be testing this later today.

This should be fixed with PureSuffering 1.6.6.1B, let me know if it works for you as well.

Thanks! It's working now

Going to close since this seems to be resolved :)