The stated error claiming that display-service.service is a symlink to gdm.serviceseems to indicate that GDM (GNOME Display Manager) is the current display manager. GDM can have issues with Wayland, especially on NVIDIA GPUs.
To disable GDM from acting as your current display manager, you can open a console as a regular user (in another desktop environment or pressing Ctrl + Alt + F5 on the login screen) and run sudo systemctl disable --now gdm. This will likely instantly end your graphical session and log you out if you did it in a GUI environment (i.e. not in a TTY console).
To now enable SDDM, you can run sudo systemctl enable --now sddm. After this, you should see the SDDM login screen (press Ctrl + Alt + F1 if you were using a TTY). If that doesn’t work, reboot and see if you can access SDDM now.
The --now flag allows systemd to start and stop services immediately. enable and disable make systemctl permanently enable or disable services starting from the next boot by default, passing --now allows changes to take place immediately. (If you just want to temporarily start or stop a service, sudo systemctl start and sudo systemctl stop are useful for that.)