https://bugs.winehq.org/show_bug.cgi?id=45899
--- Comment #21 from Konrad Materka kmaterka@wp.pl --- Let me summarize the situation, as I understand it: KDE implements proxy between xembed and SNI (using xembedsniproxy). Tray icon is rendered off screen and "duplicated" icon is sent trough SNI (D-Bus) protocol to the KDE system notification applet. Mouse clicks are not direct but emulated on the top-left corner of the wine icon. When tray icon has some transparency in top-left corner and "window region" patch is applied, mouse click is ignored by wine, probably ends up "clicking through". I don't know why it works with KDE compositing disabled.
Fix in the KDE will be tricky. The best would be to send mouse clicks where they occurred, not in the top-left corner, but it is hard to get information where notification icon is rendered on the KDE notification area.
Maybe region should not be applied on tray icons? Windows 10 is not doing that, I can click on the transparent space of the icon (or even empty space around the icon!) and it still receives the event and context menu shows at the pointer location.
Another solution would be to include this patch: https://github.com/Tk-Glitch/PKGBUILDS/blob/master/wine-tkg-git/wine-tkg-pat... It adds SNI / AppIndicator support, so that when available wine will use SNI to show tray icon. I don't know how reliable the patch is, I never tested it. As a bonus, it would be compatible with Wayland.