The answer in another thread Missing sddm.conf with KDE Plasma 6 and wayland helped me get Plasma 6 running
The recipe in the inital post seems to be missing a 3rd critical line. The example that works (just to get running) for me is:
# KDE Plasma 6
services.desktopManager.plasma6.enable = true;
# Enable SDDM, then enable Wayland support within SDDM(?)
services.displayManager.sddm.enable = true;
services.displayManager.sddm.wayland.enable = true; # required if no login diplay manager
/* # Disable X11 + Gnome.
services.xserver.enable = true;
# Enable the GNOME Desktop Environment.
services.xserver.displayManager.gdm.enable = true;
services.xserver.desktopManager.gnome.enable = true;
# Stop gdm suspending the machine if nobody is logged in to the console
services.xserver.displayManager.gdm.autoSuspend = false;
# Configure keymap in X11
services.xserver.xkb = {
layout = "gb";
variant = "";
}; */
However the keymap is wrong in Plasma, as it’s defaulting to the US keyboard layout. I assume services.xserver.xkb is not the way to configure wayland, so there’s still some config options to track down.
I read somewhere on a KDE (non-NixOS) forum that SDDM respected the system settings in /etc/default/locale. However I set the system locale to en_GB.UTF-8 during installation, but that’s not being picked up by SDDM in this setup.