When I installed 20.04 on this Dell XPS13, I got a second security password / screen lock coming out of suspend. Not too much of a problem until I try to show a video and the extra screen lock comes on at 8 minutes or so. I go thru power management settings, screensaver settings, and change the values to 60 and 120 minutes and … 8 minutes later this “new” screen lock shuts off the screen and locks it.
This wasn’t present with 18.04. It’s not on my two other computers running 20.04. How do I even find out the program that’s issuing this blank-screen command and asking for a password?
Was your system a fresh install of Lubuntu 20.04? as you mention 18.04, and upgrades from LXDE setups to LXQt without re-install can leave you with issues, which is why it wasn’t supported.
(sigh) I did this as an upgrade. I confess that I didn’t read the info about that. I’ve upgraded a desktop and another laptop, neither of which got this “double screen saver.” Since this laptop is my most-favored-system, it’s kinda painful to think about starting from a clean install.
It may help to know that the old system uses lightdm as a display manager and the new one sddm. That’s at least relevant to the initial password prompt. For lock screen, more likely light-locker (or possibly still lightdm and xscreensaver, respectively.
It may also help to know that there were instructions in the manual to remove the old system. This isn’t going to give an end result exactly like the new system, but it will be pretty darn close.