[09:45] <waveform> hi ikonia -- sorry, I was on holiday last week but I'll see if I can replicate this today (my first guess is that you'll need to add either the FKMS or KMS overlay to get this working, but it's been a long time since I tried a desktop package on focal, and about time I retried it to see what still works)
[11:26] <waveform> ikonia, unable to reproduce an issue -- tried with fresh flash of 20.04.4, all packages upgraded, then installed lubuntu-desktop with gdm3 selected as login manager. Desktop was a bit flaky without the KMS overlay, but worked. Added KMS overlay and everything mostly works fine but there's the occasional glitch where the screen blanks before coming back (may just be a dodgy adapter cable on my pi4 though)
[11:29] <waveform> ikonia, can you confirm what resolution your monitor was running at (mine here is 1080p; just want to rule out if 4K res is an issue)? Also, if you know what login manager you selected when installing lubuntu-desktop, and whether or you've got the FKMS/KMS overlay added (you won't if you haven't changed config.txt on the boot partition)