Hi! I want to ask, is it possible to load textures for model straight from textures/entity folder?

	"textures": {
	    "0": "entity/cat/all_black"
	},

My custom item but textures are broken

In modern minecraft versions, you need to specify to the game that you want a texture in the atlas for it to be added. Specifically for blocks/items you need to add the texture to the blocks atlas.

This is a vanilla resourcepack thing, there should be info online on how to do that.