It looks like you're using ModelEngine, this is currently breaking resource packs in 1.21 due to their shader files. To fix this you need to go into the ModelEngine config.yml find " Create-Shader:" and set it to false. They may still be in the files themselves, so check on ModelEngine/resource pack/assets/minecraft/shaders and remove them if needed.
A full restart may be needed to make sure things are updated correctly.
