A strange story, folks. Having upgraded Debian from Stretch to Buster, I can't run my favorite window manager. The hardware is a dual-monitor PC with Intel integrated controller (Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller). xrandr recognizes VGA-1 and HDMI-2 monitors.
- Running 'startx xterm' from command line seems to hang. The screen shows some first lines printed by Xorg during startup. However, Xorg is working. Via SSH, I can run applications (but can't see them on screen), I can make a screenshot, like this: https://imgur.com/74QFRLe. I just can't see anything. However, switching VTs causes Xorg to crash.
- I can run gnome-session and it works fine on both monitors.
- I can run startkde and it shows up, but only on one of the monitors (VGA-1), the other one remains black. It seems that an important step in startkde is running kstartupconfig5. Without it, kwin also remains invisible.
If I use gdm instead of running things from command line, I can run Gnome, old Gnome and Gnome with Xorg. Other window managers do not work, leaving only black screen.