Try checking this:
https://github.com/orgs/FabricMC/discussions/2394
#Adding item to group error 1.21.7
2 messages · Page 1 of 1 (latest)
2 messages · Page 1 of 1 (latest)
Try checking this:
https://github.com/orgs/FabricMC/discussions/2394
iirc that happens when you register your items/blocks too late, make sure to register them in your mod initialiser (or a class which you load in the initialiser)