I am having trouble with lubuntu arm (uses LXQt) on a raspberry pi 4, where the desktop is too large for the screen.
On Raspbian Buster, I am able to use 2560x1440 without trouble.
So I made sure the boot partition config.txt and related files (for lubuntu, it’s config.txt, nobtcfg.txt, nobtcmd.txt, syscfg.txt, and usercfg.txt) have the same settings as on Raspbian. I don’t think I could even choose 2560x1440 in the Monitor Settings before that.
I have not been able to make the pi 4 output 2560x1440 under lubuntu. I did get bitten by the WiFi bug (both on Raspbian and lubuntu) but disabled WiFi and worked around the problem with an adapter. So it’s not that.
Something to do with X.org configuration?
Of course this might be best posted in a raspberry pi forum, but I thought I’d start here.