Currently in NeoForge 1.21.1, enchanting an item with fireproof can only be done in creative, all items recognize it as a usable enchant in creative but refuse it in survival.

Thanks for the detailed report! I was able to reproduce this issue. Some notes:

• This happens for NeoForge 1.21.1 and 1.21
• It also happens for Fabric 1.21.1 (haven't confirmed 1.21)
• Does not happen for NeoForge 1.21.3 nor Fabric 1.21.3

Seems like the issue is the #netherited:enchantable/fireproof tag, as it is using #minecraft:shulker_boxes:

According to https://minecraft.wiki/w/Item_tag_(Java_Edition), this tag was introduced in 24w38a, a snapshot for 1.21.2. Hence, the fireproof tag is referencing a non-existent tag and breaking the enchantability

Fixed version 2.0.2 has been uploaded to both Modrinth and CurseForge. Closing