Aha! It appears this feature only works in Xorg sessions ("Ubuntu") and not in "Ubuntu on Wayland" sessions.
** Summary changed: - Vertically maximize on middle button click + Vertically maximize on middle button click does not work in Wayland sessions -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1698083 Title: Vertically maximize on middle button click does not work in Wayland sessions To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1698083/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs