For unknown reasons, the Gnome-ish
vino-server package for Xubuntu 18.04 no longer installs
vino-preferences, so it’s not obvious how to configure the server.
After considerable flailing, I installed good old
x11vnc, set up a password, then started it in
x11vnc -forever -find -no6 -avahi -usepw
I don’t mind having programs change, but it’d be nice if features like, say, configuration wouldn’t just vanish.