So obviously this is a known bug and literally every panel-like application is affected. It also seems there is no good solution so far apart from the aforementioned workaround of switching away from xinput2 via the environment variable.
** Bug watch added: freedesktop.org Bugzilla #92681 https://bugs.freedesktop.org/show_bug.cgi?id=92681 ** Also affects: greybird-gtk-theme via https://bugs.freedesktop.org/show_bug.cgi?id=92681 Importance: Unknown Status: Unknown ** Project changed: greybird-gtk-theme => xorg-server ** Package changed: greybird-gtk-theme (Ubuntu) => xorg-server (Ubuntu) -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xorg-server in Ubuntu. https://bugs.launchpad.net/bugs/1795135 Title: Window buttons are not clickable at the top of the screen To manage notifications about this bug go to: https://bugs.launchpad.net/xorg-server/+bug/1795135/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : [email protected] Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp

