Desktop not loading - tried everything but still just a black screen

[MoonRise]

Reading that and towards the end all I can ask is do you have snapd installed? Maybe purge that like suggested if you do.

EDIT: It seems Maui does have snappy installed which is from it's Ubuntu base. Perhaps that is the issue for you. I didn't even know I had that there but I also don't and probably never will use that. If you did for something maybe that set some wrong pathing somewhere?

[Enigma0]

Yeah I've read much of that bug and many other just like it and tried most things that seemed relevant that folks said fixed it for them but frankly most of the contents is gibberish to me. If anything stands out as being a good thing to try to more experienced folk I'm all ears. Tried the snapd suggestion - hadn't heard of it before the bug.

Hmm. Well not much in the log that I know about:

cat Xorg.0.log | grep EE
       (WW) warning, (EE) error, (NI) not implemented, (??) unknown.

:/var/log$ cat Xorg.0.log | grep WW
       (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[    16.205] (WW) The directory "/usr/share/fonts/X11/cyrillic" does not exist.
[    16.205] (WW) The directory "/usr/share/fonts/X11/100dpi/" does not exist.
[    16.205] (WW) The directory "/usr/share/fonts/X11/75dpi/" does not exist.
[    16.205] (WW) The directory "/usr/share/fonts/X11/100dpi" does not exist.
[    16.205] (WW) The directory "/usr/share/fonts/X11/75dpi" does not exist.
[    16.205] (WW) Hotplugging is on, devices using drivers 'kbd', 'mouse' or 'vmmouse' will be disabled.
[    16.205] (WW) Disabling Keyboard0
[    16.205] (WW) Disabling Mouse0
[    16.209] (WW) "glamoregl" will not be loaded unless you've specified it to be loaded elsewhere.
[    16.267] (WW) Unresolved symbol: fbGetGCPrivateKey

In the meantime I installed ubuntu-gnome-desktop and gdm3 and switched from sddm to gdm3 and poof, I have a desktop. I mentioned trying this in the OP but because I had autologin enabled, it didn't take.

Maybe sddm is busted?

[wizard10000]

Possible, You should be able to launch KDE from GDM3 - does it work?