Hi cramcram, under „Squeezebox Server start Installation“ >> „Alternative source from Slimdevices (package must be .deb)“ have you tried directly pasting the path to the lates 8.0 nightly? Located here: http://downloads.slimdevices.com/nightly/index.php?ver=8.0
Currently the latest would be http://downloads.slimdevices.com/nightly/8.0/lms/aaa663bb569ff4438e25c7e9a361d79b3716502d/logitechmediaserver_8.0.0~1586578181_arm.deb which is dated Apr 10.
Disclaimer – I am not affiliated with M2P and have not tried this. I would assume this is officially unsupported right now. But if I were to try it, I would first make a full backup image of my SD card before doing so. That being said, if you do give it a shot, do post results.