Thanks for your answers!
Nothing is wrong with my taskbar, there is only limitied space on my old 2nd 17“ Monitor and to be honest, once I‘ve started PSX and RT and other apps too, the most time I don‘t need the GUI during the flight and if, I could re-open it from systray with one click and let the my main apps like, P3D, Navigraph, EFB, PDF Flightplan, Webbrowser, etc. in the Taskbar.
But as I already mentioned in my initial post, no big deal - just a nice to have, and in the meantime I‘ve found a Freeware App where you simply can minimize Apps with an rightclick on the „minimize button“ in the titlebar to the systray. No need to install the app, just launch it (with admin-right) after extracting - link to the app below:
If the link isn‘t allowed here just let me know and I will delete it.
Regards and stay healthy!