This worked for me:
added the following two lines to /etc/lightdm/lightdm.conf.d/11-armbian.conf
autologin-user=<YOUR USER>
autologin-user-timeout=0
the complete file:
[Seat:*]
autologin-user=pi
autologin-user-timeout=0
user-session=xfce
greeter-show-manual-login=false
greeter-hide-users=false
allow-guest=false
Note that I also removed the password for my user (in my case 'pi')