sddm

Install xorg-server (xephyr is needed for sddm.conf)

echo "x11-base/xorg-server elogind udev xephyr xorg xvfb" > /etc/portage/package.use/xorg-server
emerge --ask xorg-server

Test sddn from commandline

sddm --test-mode

Generate sddm.conf

sddm --generate-config

Use a specifik sddm.conf file it will be executed (good for debugging)

sddm --config /path/to/custom/sddm.conf

Test sddm.conf

/usr/bin/sddm-greeter-qt6 --test-mode

Example configuration for /etc/sddm.conf

[Autologin]
Relogin=false
Session=plasma.desktop
User=

[General]
DisplayServer=x11
HaltCommand=/usr/bin/loginctl poweroff
InputMethod=qtvirtualkeyboard
Namespaces=
Numlock=on
RebootCommand=/usr/bin/loginctl reboot
GreeterEnvironment=QT_SCREEN_SCALE_FACTORS=1,QT_FONT_DPI=96

[Theme]
Current=breeze
CursorSize=24
CursorTheme=Breeze
DisableAvatarsThreshold=7
EnableAvatars=true
FacesDir=/usr/share/sddm/faces
#Font=Terminus,18
ThemeDir=/usr/share/sddm/themes

[Users]
DefaultPath=/usr/local/bin:/usr/bin:/bin
HideShells=/usr/bin/nologin,/bin/false
HideUsers=
MaximumUid=60000
MinimumUid=1000
RememberLastSession=true
RememberLastUser=true
ReuseSession=true

[X11]
#DisplayCommand=/usr/share/sddm/scripts/Xsetup
DisplayStopCommand=/usr/share/sddm/scripts/Xstop
EnableHiDPI=true
ServerArguments=-nolisten tcp -dpi 96
ServerPath=/usr/bin/X
SessionCommand=/usr/share/sddm/scripts/Xsession
SessionDir=/usr/local/share/xsessions,/usr/share/xsessions
SessionLogFile=.local/share/sddm/xorg-session.log
MinimumVT=7
UserAuthFile=.Xauthority
XauthPath=/usr/bin/xauth
XephyrPath=/usr/bin/Xephyr

Resource(s)