sometimes I review something and say "approved", but sometimes I can only review part of it, and really need someone else to check what's out of my wheelhouse.

sort of "partially approved".

I have used systems that can set things like "requires 2 reviewers" or "bob, fred are required reviewers, elon and sam are optional reviewers".

also we had "thumbs up, thumbs down, and some comments might have a "task" associated with them as a required fix before approval"

optionally, maybe before you say "approved" you have an overall comment, and see the comments of other reviewers.

In many environments that depends on more than just code review, e.g. CI.