Hi, I installed the mod only with the newest fabric API (0.69.1) and the latest cloth-config (9.0.94).
I also tested older versions of cloth-config (7.0.72-9.0.94) but the game always crashes at startup.

My installed mods, API's:

camsbackpacks-2.13
cloth-config-9.0.94-fabric
fabric-api-0.69.1+1.19.3

That's all in my mods folder, so no other mod is interfering with the backpack mod.

The log can be found here.

Regards