Useful resource if you're trying to use d-bus with Python GIO bindings. Docs are scarce about this specifically, so it helps to have an example. (probably less troublesome if you're used to the bindings generally)
https://gitlab.gnome.org/GNOME/pygobject/-/blob/master/tests/test_gdbus.py
This is also a help: https://discourse.gnome.org/t/minimal-example-of-gdbus-in-python/3165/2
The object skeleton / interface skeleton stuff is *really* extra and the more straightforward path of registering an "object", which is really just a handler function, isn't pointed out explicitly even in the C examples.