Bug#969106: gdm3 can only start a gnome session, any other (e.g. mate, icewm, gnome on xorg...) fails

[Giacomo Mulas]

Package: gdm3
Version: 3.36.2-1
Severity: important

Dear Maintainer,

I don't know exactly with which version of gdm3 this occurred, 
but with the current one I am forced to choose "GNOME" as a session
when logging in with the login manager. Any other choice just
results in getting back to the login manager. And by "any" I mean
also any other GNOME session, like "GNOME on Xorg", "GNOME fallback"...
Only GNOME (which defaults running on Wayland) successfuly starts 
a user session. Due to this, I was currently forced to install 
another login manager (lightdm) and use that, since that enables me 
to use GNOME on Xorg (quite some apps still have problems on 
Wayland). And I want to be able to use other sessions, in case GNOME
gets temporarily broken by some sid upgrade (it happened a number of
times, and being able to run MATE proved then to be absolutely 
necessary).

I would gladly produce any debugging info that may help tracing and 
solving this problem. Just give me directions on what you want me to 
test and what log files to collect and send.

Thanks, best regards
Giacomo Mulas

-- System Information:
Debian Release: bullseye/sid
  APT prefers unstable
  APT policy: (401, 'unstable'), (10, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.7.17-jak (SMP w/4 CPU threads)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=it_IT.UTF-8, LC_CTYPE=it_IT.UTF-8 (charmap=UTF-8) (ignored: LC_ALL set to it_IT.UTF-8), LANGUAGE=it_IT,en_EN
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages gdm3 depends on:
ii  accountsservice                              0.6.55-3
ii  adduser                                      3.118
ii  cinnamon [x-window-manager]                  4.6.7-1
ii  cinnamon-session [x-session-manager]         4.6.2-1
ii  cwm [x-window-manager]                       6.6-2
ii  dbus                                         1.12.20-1
ii  dconf-cli                                    0.36.0-1
ii  dconf-gsettings-backend                      0.36.0-1
ii  debconf [debconf-2.0]                        1.5.74
ii  gir1.2-gdm-1.0                               3.36.2-1
ii  gnome-session [x-session-manager]            3.36.0-2
ii  gnome-session-bin                            3.36.0-2+b1
ii  gnome-session-flashback [x-session-manager]  3.36.4-1
ii  gnome-settings-daemon                        3.36.1-1
ii  gnome-shell                                  3.36.5-1
ii  gnome-terminal [x-terminal-emulator]         3.36.2-1
ii  gsettings-desktop-schemas                    3.36.1-1
ii  icewm [x-window-manager]                     1.6.6-1
ii  icewm-experimental [x-window-manager]        1.6.6-1
ii  kitty [x-terminal-emulator]                  0.18.3-1
ii  konsole [x-terminal-emulator]                4:20.08.0-1
ii  kwin-x11 [x-window-manager]                  4:5.17.5-2+b1
ii  libaccountsservice0                          0.6.55-3
ii  libaudit1                                    1:2.8.5-3+b1
ii  libc6                                        2.31-3
ii  libcanberra-gtk3-0                           0.30-7
ii  libcanberra0                                 0.30-7
ii  libgdk-pixbuf2.0-0                           2.40.0+dfsg-5
ii  libgdm1                                      3.36.2-1
ii  libglib2.0-0                                 2.64.4-1
ii  libglib2.0-bin                               2.64.4-1
ii  libgtk-3-0                                   3.24.22-1
ii  libkeyutils1                                 1.6.1-2
ii  libpam-modules                               1.3.1-5
ii  libpam-runtime                               1.3.1-5
ii  libpam-systemd                               246.2-1
ii  libpam0g                                     1.3.1-5
ii  librsvg2-common                              2.48.7-1
ii  libselinux1                                  3.1-2
ii  libsystemd0                                  246.2-1
ii  libwrap0                                     7.6.q-30
ii  libx11-6                                     2:1.6.10-3
ii  libxau6                                      1:1.0.8-1+b2
ii  libxcb1                                      1.14-2
ii  libxdmcp6                                    1:1.1.2-3
ii  lsb-base                                     11.1.0
ii  marco [x-window-manager]                     1.24.1-1
ii  mate-session-manager [x-session-manager]     1.24.1-1
ii  mate-terminal [x-terminal-emulator]          1.24.1-1
ii  metacity [x-window-manager]                  1:3.36.1-1
ii  muffin [x-window-manager]                    4.6.3-1
ii  mutter [x-window-manager]                    3.36.5-1
ii  mwm [x-window-manager]                       2.3.8-3
ii  openbox [x-window-manager]                   3.6.1-9
ii  plasma-workspace [x-session-manager]         4:5.17.5-4
ii  policykit-1                                  0.105-29
ii  procps                                       2:3.3.16-5
ii  sawfish [x-window-manager]                   1:1.11.90-1.1+b1
ii  twm [x-window-manager]                       1:1.0.10-1
ii  ucf                                          3.0043
ii  x11-common                                   1:7.7+20
ii  x11-xserver-utils                            7.7+8
ii  xfce4-session [x-session-manager]            4.14.2-1
ii  xfce4-terminal [x-terminal-emulator]         0.8.9.2-1
ii  xfwm4 [x-window-manager]                     4.14.5-1
ii  xterm [x-terminal-emulator]                  359-1

Versions of packages gdm3 recommends:
ii  at-spi2-core    2.36.0-3
ii  desktop-base    10.0.3
ii  x11-xkb-utils   7.7+5
ii  xserver-xephyr  2:1.20.8-2
ii  xserver-xorg    1:7.7+20
ii  zenity          3.32.0-5

Versions of packages gdm3 suggests:
ii  gnome-orca            3.36.5-1
pn  libpam-fprintd        <none>
ii  libpam-gnome-keyring  3.36.0-1

-- debconf information excluded