SUMMARY STEPS TO REPRODUCE 1. Start Wayland session. 2. Open Nextcloud-desktop. 3. left-click on its system-tray icon. OBSERVED RESULT The main window of Nextcloud-destkop sometimes appears in the upper-left corner of the screen, or in the down-right corner of the screen. EXPECTED RESULT The main window should appear exactly under the system-tray icon not far away from it. SOFTWARE/OS VERSIONS Linux/KDE Plasma: KDE Neon User Edition 5.20.2 KDE Plasma Version: 5.20.2 KDE Frameworks Version: 5.75.0 Qt Version: 5.15.0
Confirmed on KDE Neon User Edition.
When you say "Main window" do you mean "context menu" or its actual main window? I ask because if it's the latter, then this is not the System Tray's fault because windows are not allowed to position themselves on Wayland; the compositor does all of that.
Its actual main window not the context menu.
Then there's nothing we can do here, sadly. The Wayland compositor chooses where to locate the window according to its own placement modes. There's support in the works for letting the compositor save and restore windows' previous positions, but I don't think that windows are allowed to position themselves manually on Wayland.