My problem with SDDM is that the majority of themes require plasma core to be installed, and I use a window manager and not a DE.
/var/log/lightdm/lightdm.log output (I think this is when I manually ran it with sudo lightdm because no logs appear if I dont manually run it)
[+0.00s] DEBUG: Logging to /var/log/lightdm/lightdm.log
[+0.00s] DEBUG: Starting Light Display Manager 1.32.0, UID=0 PID=2598
[+0.00s] DEBUG: Loading configuration dirs from /usr/share/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration dirs from /usr/local/share/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration dirs from /etc/xdg/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf
[+0.00s] DEBUG: Registered seat module local
[+0.00s] DEBUG: Registered seat module xremote
[+0.00s] DEBUG: Using D-Bus name org.freedesktop.DisplayManager
[+0.00s] DEBUG: Using cross-namespace EXTERNAL authentication (this will deadlock if server is GDBus < 2.73.3)
[+0.00s] DEBUG: _g_io_module_get_default: Found default implementation local (GLocalVfs) for ‘gio-vfs’
[+0.00s] DEBUG: Monitoring logind for seats
[+0.00s] DEBUG: New seat added from logind: seat0
[+0.00s] DEBUG: Seat seat0: Loading properties from config section Seat:*
[+0.00s] DEBUG: Seat seat0 has property CanMultiSession=no
[+0.00s] DEBUG: Seat seat0: Starting
[+0.00s] DEBUG: Seat seat0: Creating greeter session
[+0.00s] DEBUG: Seat seat0: Creating display server of type x
[+0.01s] DEBUG: Could not run plymouth --ping: Failed to execute child process “plymouth” (No such file or directory)
[+0.01s] DEBUG: Using VT 7
[+0.01s] DEBUG: Seat seat0: Starting local X display on VT 7
[+0.01s] DEBUG: XServer 0: Logging to /var/log/lightdm/x-0.log
[+0.01s] DEBUG: XServer 0: Writing X server authority to /run/lightdm/root/:0
[+0.01s] DEBUG: XServer 0: Launching X Server
[+0.01s] DEBUG: Launching process 2604: /usr/bin/X :0 -seat seat0 -auth /run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
[+0.01s] DEBUG: XServer 0: Waiting for ready signal from X server :0
[+0.01s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
[+0.01s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0
[+0.04s] DEBUG: Loading users from org.freedesktop.Accounts
[+0.04s] DEBUG: User /org/freedesktop/Accounts/User1000 added
[+0.06s] DEBUG: Seat seat0 changes active session to
[+0.86s] DEBUG: Got signal 10 from process 2604
[+0.86s] DEBUG: XServer 0: Got signal from X server :0
[+0.86s] DEBUG: XServer 0: Connecting to XServer :0
[+0.87s] DEBUG: Seat seat0: Display server ready, starting session authentication
[+0.87s] DEBUG: Session pid=2639: Started with service 'lightdm-greeter', username 'lightdm'
[+0.88s] DEBUG: Session pid=2639: Authentication complete with return value 0: Success
[+0.88s] DEBUG: Seat seat0: Session authenticated, running command
[+0.88s] DEBUG: Session pid=2639: Running command /usr/bin/lightdm-webkit2-greeter
[+0.88s] DEBUG: Creating shared data directory /var/lib/lightdm-data/lightdm
[+0.88s] DEBUG: Session pid=2639: Logging to /var/log/lightdm/seat0-greeter.log
[+0.88s] DEBUG: Activating VT 7
[+1.20s] DEBUG: Greeter connected version=1.32.0 api=1 resettable=false
[+1.52s] DEBUG: Greeter requests data directory for user redacted
[+1.52s] DEBUG: Creating shared data directory /var/lib/lightdm-data/redacted
[+3.56s] DEBUG: Greeter start authentication for redacted
[+3.56s] DEBUG: Session pid=2768: Started with service 'lightdm', username 'redacted'
[+3.57s] DEBUG: Session pid=2768: Got 1 message(s) from PAM
[+3.57s] DEBUG: Prompt greeter with 1 message(s)
[+3.59s] DEBUG: Continue authentication
[+3.63s] DEBUG: Session pid=2768: Authentication complete with return value 0: Success
[+3.63s] DEBUG: Authenticate result for user redacted: Success
[+3.63s] DEBUG: User redacted authorized
[+3.63s] DEBUG: Greeter requests session i3
[+3.63s] DEBUG: Seat seat0: Stopping greeter; display server will be re-used for user session
[+3.63s] DEBUG: Session pid=2639: Sending SIGTERM
[+3.66s] DEBUG: Session pid=2639: Exited with return value 0
[+3.66s] DEBUG: Seat seat0: Session stopped
[+3.66s] DEBUG: Seat seat0: Greeter stopped, running session
[+3.66s] DEBUG: Registering session with bus path /org/freedesktop/DisplayManager/Session0
[+3.66s] DEBUG: Session pid=2768: Running command /etc/lightdm/Xsession i3
[+3.66s] DEBUG: Creating shared data directory /var/lib/lightdm-data/redacted
[+3.66s] DEBUG: Session pid=2768: Logging to .xsession-errors
[+3.66s] DEBUG: Activating VT 7