If you are in spirit form, and you are underwater, it looks like you have an oxygen bar. This only applies if #250 is also in effect.

To reproduce:

1. Create a new world with cheats enabled.
2. Get yourself in spirit form.
3. /execute in the_nether run tp @p ~ ~ ~
4. /execute in overworld run tp @p ~ ~ ~
5. Go underwater.
6. Notice that you have an oxygen bar when you shouldn't.
7. Possess something, then go back into spirit form.
8. Go underwater.
9. Notice that you now do not have an oxygen bar.

Modlist (MC 1.16.5):

Mods:
  [✔️] fabric-api-0.29.3+1.16
  [✔️] modmenu-1.14.13+build.19
  [❌] requiem-1.4.4.jar (disabled)
  [❌] requiem-1.5.0.jar (disabled)
  [❌] requiem-1.6.2.jar (disabled)
  [❌] requiem-1.7.0.jar (disabled)
  [✔️] requiem-1.7.6
  [❌] requiem-pandemonium-1.4.4.jar (disabled)
  [❌] requiem-pandemonium-1.5.0.jar (disabled)
  [❌] requiem-pandemonium-1.6.2.jar (disabled)
  [❌] requiem-pandemonium-1.7.0.jar (disabled)
  [✔️] requiem-pandemonium-1.7.6