noctalia-greeter default session matches desktop file Name=

noctalia-greeter's [session] default key is matched against the Name= field of the session's wayland-sessions .desktop file, not its filename or binary. Name= can be capitalized (e.g. Name=Umbriel while the file is umbriel.desktop). Look up the exact Name= in <pkg>/share/wayland-sessions/*.desktop before setting it. Changing the greeter default does not cover other launch paths, such as a tty1 fish loginShellInit that execs a compositor session or a greetd initial_session in a NixOS vmVariant, so check for those as well.