Ubuntu 24.04 won't start display manager. Can only be used properly from remote session

Question

Recently I changed desktop environment from GNOME to KDE and back while I was connecting to my Ubuntu 24.04 PC remotely with XRDP, whereafter my PC won't load display manager and is practically "bricked" on local session, but works properly on remote session.

Here's a summary about what I have done and what went wrong:

• While connecting to my home PC (Ubuntu 24.04) remotely with XRDP, I installed KDE Plasma desktop from Synaptic, and changed DM to SDDM when the prompt showed up.
• When I get back home and tested the new desktop locally, I realized a bug still presists (clicking "shut down" or "restart" from KDE will freeze the desktop. I have to switch to TTY to shut down the PC. -- Something in shut down script from KDE doesn't work). So I discarded the plan to switch to KDE, changed the DM back to GDM3, and restarted the PC.
• After reboot, GDM crashed immediately, showing me the GNOME sad face crash screen. The TTYs are not loaded either, showing a black screen when I Ctrl+Alt to any TTY.
• I tried to log in to my PC remotely via XRDP. Login succeeded but I was greeted with another GNOME sad face crash screen. This time the screen is in dark mode instead of having white background from GDM crash, meaning this was a crash screen from GNOME shell.
• I thought GNOME settings must have went wrong, so I installed Xfce4 through SSH shell, changed the DM to LightDM and removed GDM3.
• After the first reboot, everything was fine and I could log in to Xfce4.
• After the second reboot however, Ubuntu stucked at Plymouth session because it's waiting indefinitely for LightDM to load, which keeps failing.
• systemctl status lightdm.service just stated Start request repeated too quickly and Failed with result 'exit-code'
• As with GDM crash, no TTY could be loaded and I had to use remote access to get into my PC. Unlike GNOME, Xfce4 works properly in the remote session.

So it seems that the display managers get messed up. Whatever DM I choose, it would work one reboot after the configuration but then fail.

Could it have something to do with me having configured the DM from a remote computer with different screen resolution than my PC? If this is the case, how can I configure the DM to use my local display settings?