The Skybox is visible instead of being clouded by the underwater fog, tested the issue on Java Edtition 1.17.1 and 1.18.1

Can reproduce, the bug seems to be fixed by Sodium somehow. Not sure why yet, but it works as a temporary fix to this issue.

which version of sodium fixes the issue?

This is now confirmed to be vanilla behavior, simply rearing its head in an ugly way. #45 fixes this, however the verdict of whether the behavior will be kept is still unclear.

Should be resolve in ea4724e, this will be available in the next release.