Minecraft 1.19.3 dropped support for resource packs for 1.7-1.12. For example, 1.19.3+ won't recognise textures/blocks/wool_colored_yellow.png for a yellow wool block. Only the new path, which is textures/block/yellow_wool.png, is recognised. This mod brings back old resource pack support in 1.20.

The resource pack format should be less than 4 to work.