Implement org.freedesktop.ScreenSaver
The Phosh session exposes 2 dbus services for the screen saver, with differing behaviour (see https://gitlab.gnome.org/World/Phosh/squeekboard/-/issues/355#note_1613814 ).
However, both services expose pretty much identical functionality, compare: https://lists.freedesktop.org/archives/xdg/2006-June/006523.html and https://lists.freedesktop.org/archives/xdg/2007-March/009187.html .
The "freedesktop" service seems to be dead.
This means that applications binding to the general (freedesktop) one first will successfuly find it and try to use it, but will not actually be connected to any behaviour they expected.
Filing in os-issues because I don't know better.