Back to my Python DBus experiments in Linux, I still can't call the Freedesktop Notifications interface using Gnome. It works seamlessly on KDE Plasma, but on Gnome every call throws an exception stating it can't find the method, even though it's name shows in the interface introspection, with the correct signature, as found in the Notifications specification:
https://specifications.freedesktop.org/notification/latest/protocol.html
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