The issue occurs when you try to use the quiver from supplementaries in the accesories gui. After you ctrl+right-click the quiver in the gui, the game crashes. It says it didn't find the slot or smth like that.

log: https://mclo.gs/H4iLcgL

Support for 1.20.1 is being dropped and I recommend investigating if the issue exists with this mod on 1.21.1 if possible with either reopening this issue or creating a new one.