Global shortcuts code implemented the initial protocol, but it was
changed in
https://github.com/flatpak/xdg-desktop-portal/commit/8cb5b6d997108443ecc26152c95bbca8c8c58fc3
to move shortcut changes only to BindShortcuts from CreateSession.
Matching changes to xdg-desktop-portal-kde in
plasma/xdg-desktop-portal-kde!274