[Nix-dev] Can't launch XFCE from SDDM?

[Karn Kallio]

The treats the exec argument of the .desktop files not as
a command but as a parameter to pass to the session command.  For
SDDM this can be observed in the file src/helper/UserSession.cpp.  The
NixOS xsession has been modified to handle this difference as a special
case.  The same thing happens with KDM, but the special casing is
slightly different.  It might be that in your version of NixOS the
xsession has been special cased for KDM and not SDDM.  With the recent
removal of the older KDE the special case was changed to work with SDDM.