Where to set the default plasma-session?

Running Debian 12, with plasma 5.27.5 and sddm 0.19.0-5. I need to run several applications that don’t work with Wayland - call them legacy, if you must - so I want to set the default session to X11. I know it must be possible, because I can choose 'Session: Plasma (X11) on the login screen, which means it is supported and the default session type is loaded as an option somewhere (rather than being hard-coded - I respect the developers too much to believe they would hard-code something like that).

I have found what looks a lot like where either session gets started:

root@jan:~# grep startplasma /usr/share/*sessions/*
/usr/share/wayland-sessions/plasmawayland.desktop:Exec=/usr/lib/x86_64-linux-gnu/libexec/plasma-dbus-run-session-if-needed /usr/bin/startplasma-wayland

The remaining question is, I suspect: where is the default that chooses Wayland over X11?

Are you saying you select “x11” on SDDM and you still log into wayland?

Please confirm with echo $XDG_SESSION_TYPE

If you selected x11 and above shows wayland it is a bug.

No, that works fine, but since I’m always going to use X11 it makes better sense for me to have that as the default. It is very easy to log in without remembering to change to X11, then start up a number of heavy applications until something turns out not to work; it is very frustrating in that situation to have to shut everything down, log out and do it all over, just because I can’t set X11 as the default.

I can probably track down where this set, eventually, but I’m hoping one of the kind developers could point me in the right direction - I’ve already spent too much time on this, really, but it is actualy important to me.

IMHO a very bad idea since x11 support is slowly being dropped all over.
Use Xwayland for x11 apps that are not ported. (when you become forced to use wayland, in a few years, until then, just keep using x11)

What do you mean?
If you select x11 in SDDM it will STAY x11.
Does the dropdown on SDDM change by itself?
If so, report it to SDDM as a bug.

Really? Yes, you are right! That all I need - I wonder where I got that idea from, that it changed back… But I have been reinstalling this particular laptop seevral times recently, trying out some things I’m working on, maybe that confused me.

But thank you for opening my eyes!