I updated yesterday my Debian (i use Debian Testing with XFCE) and in the update progress the linux image was upgraded to linux-image-4.19.0-4-amd64.
After a reboot , Debian was not capable to start graphical environment.
I end up with a single dash in the upper left corner.
Though i was capable to switch to tty1 using ctrl-alt-F1 , log in as root and create the attached log files.
I am not sure if i should assign this bug to linux package, or display manager or xserver, but when i boot using the previous kernel (linux-image-4.19.0-2-amd64) everything works perfectly and my debian starts with XFCE.
As such i suppose this bug is related to the recent kernel update.