For our team we do a series of reviews with a lower level engineer, then send it up to our lead engineer to review, at this stage it can go back and fourth several times until something is merged in.
Typically, a very junior engineer reviewing code for another junior engineer isn’t sufficient. We may require two sign offs before the code is merged.
Senior+ engineers review critical path code, but not every single code review. This is to create space for others and also ensure others are not merely spectators but actively own what’s going on.