I think this page should note that now PHP 7.4 is required (and probably the level of PHP 8.0/8.1 support; where are we yet?). I don’t know where to put and how to formulate this piece of information, though, so if anyone can include it, thanks in advance!
Topic on Talk:MediaWiki 1.39
Yeah, this page and the main release notes page have both been filled out prematurely, and miss out on the wording. We'll probably re-sync them when we're pushing the actual release.