As of 1.21.4, extra models registered through a ModelLoadingPlugin only load the top model. If the model has a "parent", it is not loaded, resulting in a blank model. This works in Minecraft versions before 1.21.4, but Fabric API has seemed to have lost that behaviour during the update.

is there a way that they will fix it or is it just how fabric will be now lol

This appears to be vanilla behavior in 1.21.4

It will load but not bake parents that are unused otherwise. You can see this by trying to read any of the templated models like cube_all. they are not baked.

This is a bug. I ported Model Loading API v1 to 1.21.4 but this issue was not brought to my attention; I happened to stumble upon it now. Expect a pull request to fix this soon.

Fixed with Fabric API 0.114.1.

oh awesome