What you describe is standard merge request practice in Gitlab (it is possible to view the diff between different force pushed ”versions” of the branch as well).
GitHub is hostile to rebased PRs, going as far as erasing commits not present in the latest version of a PR. It does record a "... was force pushed from commit xxxxxx to xxxxx" in the PR's chronology though; but if you click on the first commit in that message it shows a 404.
Good to know, we use GitLab and occasionally would use that. I tried it a couple of years ago on GitHub, and it seemed to break the UI. I read it got a bit better now.
Don’t know about Github.