As of 1.20.5 pre-release 1, mobs from ominous trial spawners now have a chance to spawn with enchanted armor. However, despite being mutually exclusive, mobs do spawn with the three possible types of protection (projectile, fire and protection) in all armor pieces, instead of only spawning one type of protection per piece.

How to reproduce

1. Enter a trial chamber.
2. Drink a bad omen potion.
3. Trigger a zombie spawner.
4. Execute the command on a zombie with enchanted armor (in this case, helmet):

   /item replace entity @s armor.head from entity <mob's uuid> armor.head
   

   Alternatively, use this command to check for the armor items:

   /data get entity <mob's uuid> ArmorItems
   

5. Notice how the helmet you have (or the mob has) equipped has all protection enchantments.

Expected result
Mobs would only have one of the three protection enchants in the armor piece.

Observed result
All possible protection types are applied despite being mutually exclusive.