I think so

Cause we usually find salt deposits which we can eat

And the only edible salt i know is NaCl with other minerals

SO i think subnautican oceans have nacl

(NaCl Sodium chloride is a type of edible sault)

And we get nacl from our oceans

If you have other questions feel free to ask me

https://en.wikipedia.org/wiki/List_of_edible_salts here's a list of edible salts to contemplate over

O-o

If you look at the in-game description of the salt deposit, if says NaCl, so yes the same salt that’s in our oceans.

What about the atmosphere in the game? What's the proportion of nitrogen to oxygen?

I’d assume similar to Earth’s as well.