Upgrade to 20.04 caused auto-login to be set, cannot change desktop env

[dhfx]

About a month ago I successfully (or so I thought) upgraded Ubuntu 18.04 with (separately-installed) LXDE to 20.04. Subsequently I accepted an "upgrade" requiring a reboot, and when I rebooted I found that auto-login had somehow been enabled, bypassing the login screen which offers a choice of desktop session types.

I have since (in a previous thread) learned that the LXDE that I installed under 18.04 is not compatible with 20.04, so I purged it (as much of it as I could) and installed XFCE - anything to get away from the default Gnome desktop. But without the login screen I have no way of switching to an XFCE session.

My user account (GUI) does not show auto-login enabled. So what I want to do is find a way to either (1) disable auto-login from the command line, or (2) set the default desktop environment from the command line, by editing the appropriate config file.

Any suggestions will be appreciated.

[Xian]

Can you run the command below so we can confirm your display manger:

$ cat /etc/X11/default-display-manager

For example:

cat /etc/X11/default-display-manager
/usr/sbin/lightdm

[dhfx]

$ cat /etc/X11/default-display-manager
/usr/sbin/gdm3

[deadflowr]

Check /etc/gdm3/custom.conf.
You should have entries for

AutomaticLoginEnable=True
AutomaticLogin=username

either remove those or add a # symbol to the front of them to disable.
(Or edit it and change True to False)

Then try reloading gdm

sudo systemctl restart gdm3

and see if it stays on the login screen long enough to switch desktops.

[dhfx]

Apologies for delay in responding. I looked at /etc/gdm3/custom.conf, and it has both of the AutomaticLogin lines, and BOTH are commented out.
Edited /etc/gdm3/custom.conf to uncomment & set
AutomaticLoginEnable=False
and ran cmd
sudo systemctl restart gdm3
Cmd had no effect. Rebooting also showed no change in behavior.

Anyone have any further suggestions?

[deadflowr]

Switch display managers.
install another like lightdm then reconfigure the system to use that one
Try

sudo apt install lightdm

then run

sudo dpkg-reconfigure gdm3

it will show entries for all installed display managers.
select/highlight lightdm and select Ok

Then reboot.
If done properly you will have Ubuntu's old unity-greeter.
The sessions can be selected by clicking on the icon in the username login box's top right corner.
(The default icon should be Ubuntu's logo)