Shulkerboxes with Fire Protection still burns after placing down and picking up, rendering them kinda useless.
However it seems like this could potentially be a feature quite hard to implement, if that's so then just implement to shulkerboxes or a limited set of blocks

I don't think this is in-scope for Fabrication.

I'd imagine tricking the server into thinking that players are in creative mode, therefore enabling players to bam the enchantments on the anvil.
However, keeping blocks enchanted after placing down would be painful

Shulker Boxes aren't enchantable in vanilla and therefore can't accept Fire Prot with just Fabrication; whatever mod you're using to add enchantments to shulker boxes is hardcoded to keep only its enchantments.

I wouldn't quite call that a bug in the other mod, but it makes the logic of putting shulker box enchantment code into Fabrication questionable. This would fall under a separate tweak that also makes shulker boxes enchantable.

Doing this generically for any block that happens to be enchantable would be very painful and hacky.