Sorry, when I saw suffocation, I thought of suffocating in a wall, which protection does nothing against. Not sure if that’s a bug or not.
I just made sure, In the newest update for Bedrock edition, v1.17.32, protection Does NOT apply it’s defense boost for suffocation, taking the same amount of damage with full protection 4 as you would with no armor at all.
Sorry, when I saw suffocation, I thought of suffocating in a wall, which protection does nothing against. Not sure if that’s a bug or not.