Open the tab of "Files changed" in a Github PR:

Open the dropdown "Changes from all commits":

Then hold [Shift] and click a commit inside the dropdown. Then click again at another commit. The yellow-highlighted items is the range:

Then you'll be redirected to a PR's view containing a diff only from the range of the selected commits.

If you really feel like buying me a coffee

... then feel free to do it. Many thanks! 🙌