In prior versions, block/item models could access a texture directory outside of the default directories in the texture folder (block, item) if it existed.

in a working resource pack in 1.19.2, all my custom textures were stored under textures/custom/_, I assume because "custom" is not a native member of the textures folder, the game no longer recognizes it.

on a side note as well, I have a model that overrides the minecart item texture and uses the texture under textures/entity/minecart. this also no longer works either but does in 1.19.2