change pack.mcmeta to "max_inclusive": 57 just so it doesn't give an incompatible version warning in singleplayer. Suggest this tool to migrate old resource packs to 1.21.4+ (yes it works wonders) ...

To experience something new in Minecraft, you can install data packs. The data packs enhance your gameplay experience by adding new features. As of 2023, the Minecraft community has created many ...