Fedora 32 : Change display manager.

The display manager is a graphical login manager which starts a session, simply asks username and password to login desktop.
On Fedora, you can choose for example GDM (Gnome Display Manager), SDDM (Simple Desktop Display Manager), LXDM (LXDE Display Manager), LightDM, KDM (KDE Display Manager), XDM (X Display Manager).
I like the old gdm display manager, is good and works great.
If you want to change it then use these commands:

[root@desk mythcat]# dnf install gdm
...
Complete!
[root@desk mythcat]# systemctl disable lightdm 
[root@desk mythcat]# systemctl enable gdm
Failed to enable unit: File /etc/systemd/system/display-manager.service already exists and is a symlink to /usr/lib/systemd/system/sddm.service.
[root@desk mythcat]# systemctl disable sddm.service 
Removed /etc/systemd/system/display-manager.service.
[root@desk mythcat]# systemctl enable gdm
Created symlink /etc/systemd/system/display-manager.service → /usr/lib/systemd/system/gdm.service.
[root@desk mythcat]# reboot

If you have problems with gdm display manager then you can read about settings here.
The configuration file can be found in this file:

[root@desk mythcat]# cat /etc/gdm/custom.conf 
# GDM configuration storage

[daemon]
# Uncomment the line below to force the login screen to use Xorg
#WaylandEnable=false
AutomaticLogin=mythcat
AutomaticLoginEnable=False
[security]

[xdmcp]

[chooser]

[debug]
# Uncomment the line below to turn on debugging
#Enable=true 

Fedora 32 : Repair the starting LightDM display manager.

LightDM is a cross-desktop display manager with these features:

• Cross-desktop - supports different desktop technologies.
• Supports different display technologies (X, Mir, Wayland ...).
• Lightweight - low memory usage and high performance.
• Supports guest sessions.
• Supports remote login (incoming - XDMCP, VNC, outgoing - XDMCP, pluggable).
• Comprehensive test suite. 
• Low code complexity.

To start it you need to use these commands:

[mythcat@desk ~]$ sudo systemctl get-default
[sudo] password for mythcat: 
multi-user.target
[mythcat@desk ~]$ sudo systemctl set-default graphical.target
Removed /etc/systemd/system/default.target.
Created symlink /etc/systemd/system/default.target → /usr/lib/systemd/system/graphical.target.

Restart your Fedora distro and use it.