Some notes about Lightdm and the actual packaging/dependency situation in Fedora Linux.
After an upgrade from F38-39 Lightdm was not starting anymore (See discourse link below). https://discussion.fedoraproject.org/t/what-happend-to-lightdm-i-tougtht-it-is-light-installed-160mb/98430
There are a lot of tutorials in the internet where shows how to change the config Files of the Lightdm Display Manager. Example = https://christitus.com/lightdm-configuration/
This tutorials are mostly working well on Debian based Distributions. Fedora goes a different approach.
Installing lightdm in Fedora Linux
The Display Manager has to be enabled or disabled if you want to change to a other one.
Check which Display Manager is active with
grep 'ExecStart=' /etc/systemd/system/display-manager.service
The result looks like this = ExecStart=/usr/sbin/gdm
Install the new DM like sudo dnf install lightdm-gtk
Disable & enable:
systemctl disable gdm
systemctl enable lighdm