Fixed issues regarding uncraftable and unusable backpacks, these issues should be fixed now.
However, Mojang changed how CustomModelData works in 1.21.4, so the resource pack is completely broken and won't work. The plugin should still work as intended, but of course you don't have textures or colored backpacks.

When I get a tad more time to look into resource packs, I will make an update, but that will probably conclude the plugin for < 1.21.4, since the code has to change a bit and won't work for older versions anymore (unless i find a workaround :3)