In situations where I'm doing PR reviews seriously in a multi-developer environment I'm usually on Gitlab. Gitlab definitely has some features for this sort of thing, but I've never been able to use them seamlessly or quickly.
I was at one point considering writing a tool which would checkout an MR, then let you just edit it as per normal, and then would submit the whole thing back to a Gitlab MR as a set of proposed changes. The point was to ensure that you could easily expand the MR beyond the diff of changed lines, which was frequently inadequate to review a patch properly since it omitted context.
