After extensive search I was not able to see a zombie nautilus spawn.
I know they should appears when a drowned carries a Trident in a ocean. I saw 40+ of drowned with a trident and none was on top of a Zombie nautilus.
I also try to make them spawn with drowned egg. I saw drowned chicken jockey but no nautilus zombie.
This issue is not new to this version in all of the snapshot no zombie nautilus spawn
Environment
Minecraft JAVA solo world
they can spawn just fine in my world, type
/tp @n[type=zombie_nautilus]near ocean ruins, you will eventually see some spawning