Minecraft wiki entry for Damage, associated text: A squid, glow squid, or any kind of fish suffocates in air instead of drowning in water.
Dolphins can suffocate in air or drown in water and must be given access to both to survive.
Aquatic mobs, iron golems, skeletons, strays, zombified piglins, and zoglins are immune to drowning.
A zombie can drown but does not take damage; instead, it begins the process of converting to a drowned mob when continuously in water for 30 seconds.
Similar to a zombie, a husk does not take damage from drowning, but first converts into a zombie, which then converts to a drowned if it remains underwater.
A wither can drown, but it breaks blocks around it (including water) upon taking damage.