/etc/lightdm/lightdm.conf.d/50_budgie-desktop.conf is in budgie-lightdm-theme-base 0.9.6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | [Seat:*]
user-session=budgie-desktop
allow-guest=false
|