In previous versions, you could apply the unbreaking enchant to tools with the Unbreakable:1b NBT. This was very useful for custom durability tools in datapacks and maps which is no longer possible.

Since 24w03a and beyond the unbreaking enchantment is unable to be applied via anvil (in survival) or /enchant. I am reporting this as a bug as it was not listed in change notes and only happened around the time that the enchantment registry changed.