@jamie-2 the suggestion worked but of this way;
[Service]
# temporary safety check until all DMs are converted to correct
# display-manager.service symlink handling
ExecStartPre=/bin/sleep 10
ExecStartPre=/bin/sh -c '[ "$(basename $(cat /etc/X11/default-display-manager 2>/dev/null))" = "lightdm" ]'
ExecStart=/usr/sbin/lightdm
Restart=always
BusName=org.freedesktop.DisplayManager
@jamie-2 the suggestion worked but of this way; manager. service symlink handling /bin/sleep 10 /bin/sh -c '[ "$(basename $(cat /etc/X11/ default- display- manager 2>/dev/null))" = "lightdm" ]' /usr/sbin/ lightdm org.freedesktop .DisplayManager
[Service]
# temporary safety check until all DMs are converted to correct
# display-
ExecStartPre=
ExecStartPre=
ExecStart=
Restart=always
BusName=