after a fresh installation of the latest xfce-edition on the low budget notebook of my wife, the light-dm failed to start. Only an error message appeared on the TTY. A manual start from a different terminal was successful.
I found a solution in the official arch-wiki in page LightDM, which works fine for me:
from 6.8 LightDM does not appear or monitor only displays TTY output
Maybe it will be useful to set this as default? I think that wouldn’t blow up the startup time much, but could avoid some getting-started frustrations?