As of this April, ish, gnome-python-desktop is not included in Bionic Beaver's repositories (https://bugs.launchpad.net/ubuntu/+source/gnome-python-desktop/+bug/1739797), and neither are its dependents - including python-rsvg. As such, installing winswitch from the apt repository no longer works. Please advise.
This is xpra's bug tracker, looks to me like you want winswitch bug tracker instead.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1958