You can review a PR commit by commit. But it's not obvious how in the UI. Navigate to the commits tab on the PR page and you can navigate through the commits in the PR and review them one by one. Although it's possible this isn't what you mean.
Github doesn’t understand that all commits can change for review purposes. This is what makes it a ‘toy’ (though I prefer stronger wording here.)
Right, the problem is when I amended one of my patches there's no way for the reviewer to look at a diff between current and previous versions.
ADO handles this by showing a dropdown of 'comment left on update X, currently update Y' with a toggle to show the difference.
I ~hate how ADO handles individual commits (comment left on a single commit is hidden), but I do like the update tracking on a PR as it allows cleaning up the commit tree seamlessly without losing history or comment traceability (less you remove/move files).
Indeed. I wrote a tool for myself to help with that in my reviews: https://github.com/nhaehnle/vctools/tree/main/diff-modulo-ba...
It admittedly doesn't have a lot of polish, but I do use it regularly and I'd be happy to help anybody who is interested in using it.