So… I tried the whole leapp upgrade thing. It basically was a total disaster. (not a reflection on foreman/katello, but rather the redhat tools). Left my system like a block of swiss cheese, with a bazillion package conflicts and so on. It was worth a shot but for me… NOPE.
I ended up doing a full backup (which I already had set aside), wiped my system clean, installed Rocky 9 (was Rocky 8…), and restored. As before, that just… WORKED.