boot – Can’t log in to Gnome session

Since just now, I booted (I will number this boot (-1)) and I cannot log into a Gnome session. I have Ubuntu 20.04.3 LTS.
The problem: Entering my password, flashes the screen as it would do in a normal login to display my desktop, but instead it brings me back to the login screen.
Login fails with any of the two users (see below), so I guess it is not something related to any of the users, that I could solve by logging in in a console and mv ~/.config ~/.config-old + rebooting.

This is a timeline of what happened

  (A)      (B)      (C)             (D)              (E)          (F)                 (E)
  work     (-2)     some       login ok VT1    failed login VT1   (-1)   failed login VT1 + No X VT2
normally          tinkering     both users        both users                both users       

and I will describe it next.

  • I was working normally (A), rebooted (B) = (-2), and still working normally.
    I had only user user1 that I used for everything.

  • At (C) I created user guest a couple of days ago, to test something about login screens (and the failure may be related to this).
    I was logged into a gnome session with user1 in virtual terminal VT2 (Ctrl+Alt+F2) and I could work normally.
    I could log in normally with both users in VT1 (Ctrl+Alt+F1) as well.
    I was testing killing the sessions in VT1 with killall -3 gnome-shell and related commands, but still did not see any problem (D).

  • At some point (E) I started seeing in VT1 the problem above. I do not know what I did in between (D) and (E), perhaps some of the commands tested generated the problem.

  • After sleeping the PC and resuming, it was frozen, so I cold booted it (F) = (-1).
    I slept / hibernated / resumed the PC a few times before, in between (E) and (F).

    Now VT1 has the problem, and VT2 only gives me a console, not an X session.

So I have two terribly combined problems: (1) non-functional X session in VT1, (2) no X session in VT2.

I mean to solve both.

Solving #2 could at least make it much easier working to solve #1, within an X session in the same PC that I have the problem.
My attempt: Logging into VT2 and running

$ startx -- :0

(or :1) gives me

xinit: giving up
xinit: unable to connect to X server: Connection refused
xinit: server error

Further possibly relevant info:

  1. Up until boot (-1), VT2 was shown on startup, and this is my experience with all Ubuntu’s I installed since a few years ago, probably all after the change of layout of X sessions / consoles). Now VT1 is shown on startup.