Why I think?
I Think Why Is Incompatible is because It says fancy menu and Legacy4J in the .txt

Log Files
Log.zip or
https://gist.github.com/BypassSysZombie/edb5fdfca0bebbbaec2765fae597c4ee

Screenshots

Basic Informations

• OS: Windows
• FancyMenu Version: 3.3.2
• Forge/Fabric Version Fabric 0.16.7
• Minecraft Version 1.21.1
• Active Mods JEI ,Legacy4J,CraftedCore,Walkers,wthit,xaero's Minimap, Xaero's World Map,SkinShifter,Forge Config api Port,inmersivemc,konkrete,legacy skins,sit

Legacy4J changes lots of menus. It will probably never be compatible with FancyMenu.