As mentioned in
https://bugs.kde.org/show_bug.cgi?id=365308
because of
https://cgit.kde.org/plasma-workspace.git/commit/?id=27b1030756002e91b60ba51483efe9c2c477d16e
we regressed on
https://phabricator.kde.org/R120:5d5518455d10406292495c6e6874eeeb7c4534f1
This patch is supposed to fix it again. Look into the bug report if you're interested in finding a better solution in general (i.e. opening the window directly instead of only showing the context menu - XFCE is able to apparently!).