Relates to MC-262692.
The bug
23w45a introduces the template model cube_all_inner_faces.json, used for hollow-looking blocks like spawners. It appears that powder snow has not been updated to use this model, meaning it instead continues to pointlessly define its own model, resulting in a much larger file size than is necessary.
How to fix
Make powder snow reference cube_all_inner_faces.json instead. An example of a fixed model file is attached.
If you use this fix the fog effect inside the powder snow blocks is applied to the incorrect faces.
Edit: Oh, well, the problem is MC-266463. With the culling problem corrected the fog effect works correctly with your fix.