You have tried adding 'nomodeset' to the grub boot line, so it is not your video driver. You have renewed your .Xauthority file, so it is not a permissions problem...
At the Grub Boot Menu, using the same method for editing the Linux Kernel Boot line, adding and trying 'nomodeset'... You could alternately try the boot parameter 'amdgpu.dc=0', then <Cntrl><X> to continue the boot process to see if that helped... But I am thinking, try that next, if that doesn't help, then we need to go on and dig deeper.
The order of installation and connections of is as follows:
- Display Engine (XServer or Wayland),
- If Xserver, then Xinit...
- DM (Display Manager [the graphical login manager]- SDDM. etc.)
- DE (Desktop Environment- Plasma, etc.)
I have a plan. I think the connections between the pieces of might have gotten 'confused'. Each part of this plan, starts from the least invasive to more invasive...
In the first part of the plan, try
Code:
sudo dpkg --configure -a
This will try to reconfigure all that is installed... It knows the order it needs to do things, and how. Let it go through everything them. On successful completion, reboot to test... if that does not work, then on to the next step....
Next would try to reconfigure each piece in order
Code:
sudo dpkg --configure xorg-xserver
sudo dpkg --configure xinit
sudo dpkg --configure sddm
sudo dpkg --configure plasma-desktop
This does the same as above, but tells it to do it in the order, We are telling it, to those specific packages... On successful completion, reboot and test. If that doesn't work...
What I am thinking,and have seem work, it that if you reinstall the pieces of your graphics layer, in order, then it will reinstall everything needed to get everything reconnected (including the soft and hard links).
What I do not know is the desktops you may have installed...
Code:
ls /usr/share/xsessions/
That will list all your installed desktops.
Then do
Code:
sudo apt update
sudo apt install --reinstall xorg-xserver xinint
sudo apt install --reinstall sddm
sudo apt install --reinstall plasma-desktop
Which will reinstall XServer, xinit, sddm and plasma.desktop in order... At successful completion, reboot and test.
If at any time, if one of those commands do not complete 'successfully', stop and post the error, and we will go from there to resolve that.