On a KDE Wayland session a screen sharing dialog pops up continually any time you try to access a menu item, and choosing the output to share does not seem to have any effect or "stick", preventing access to the menu.
As a workaround, the Designer can be started with -Dawt.robot.screenshotMethod=x11, which will simply cause the screen sharing attempt to fail rather than invoke this new dbus sharing request code path that doesn't seem to work on KDE.
https://bugs.openjdk.org/browse/JDK-8307456
https://bugs.openjdk.org/browse/JDK-8280982
and related