It seems that you removed menu integration classes when backporting from 1.16, but left the entrypoint for it in fabric.mod.json. So it throws java.lang.ClassNotFoundException: autoswitch.modmenu.ModMenuImpl.
I commented out the modmenu entrypoint in the jar and it fixed the problem.
It seems that you removed menu integration classes when backporting from 1.16, but left the entrypoint for it in
fabric.mod.json
. So it throwsjava.lang.ClassNotFoundException: autoswitch.modmenu.ModMenuImpl
. I commented out the modmenu entrypoint in the jar and it fixed the problem.