logind: Activating session/opening seat fails in systemd v254

[Nils Kattenbeck <nilskemail@xxxxxxxxx>]

Hi everyone,

I am working on a kiosk-type device which is supposed to start a
weston instance upon boot.
Our images were previously based on Debian 12 and Fedora 38, now we
are working on unifying them. Between the two old image variants the
systemd units were mostly identical, however, on Fedora 39 with
systemd 254 they no longer work. Weston/libseat now fails with the
message: "Could not activate session: Permission denied". (Also see
the logind logs at the end).

I have been looking through the NEWS file and release announcement to
see if I could spot any change which could have this impact but
nothing stood out. Maybe someone else has a clue and remembers any
recent change. This must have been a change between v253 and v254 as
Fedora 38 is using the former and f39 is using the latter.

Any help would be appreciated as I have worked on this for a few days
now without success. (I can also try to create a MWE and publish the
repo. It is build using mkosi so reproducing should be easy.)
Kind regards,
Nils