Hello maintainer, here i have the same problem after upgrading a server with XFCE from Debian 9 to 10 and then to 11.
After the upgrade there is only a blinking cursor on the monitor. I already did make an reinstall of the package lightdm. The X-server and XFCE is working. I have to get an user console with Ctrl-Alt-F1 and the login with the user. After that i can call startx to start the X-Server and XFCE. This package is unusable now. Please help to solve the problem. Best regards karsten