1.21.4-1.21.8 CUSTOM DP/RP Help needed updating!

Heya! I just wanted to join and ask some folks for help... A while ago I had coded a custom music discs + a few items / sounds retextures + custom crafting recipes + mob drops datapack/resource pack for my personal SMP server. It works wonderfully on 1.21.4 (the version it was programmed for), but I can't for the LIFE of me manage to get it to not break in 1.21.8 / any newer version. The datapack has become a really key component for teh server, so we don't wanna update it until the pack can be fixed... Anyone who may be able to help? Could peek at my code and tell me if they see the issues? Etc... I haven't found any help online D:
(Please make sure to ping me if you reply! May not see it otherwise lolol)