Previously I had QtCreator 4.15.2. Last week I upgraded to 6.0.1 and now I can't start my application. All I get is the following dialog window. "Application output" pane is empty.

Again - I've been using 4.15.2 for more than half a year and everything was working correctly.

For "Platform" I chose "Other display system" because I don't know whether Kubuntu is still using X11 or already switched to Wayland. Besides this error is clearly unrelated to graphics. I checked and Kubuntu 20.04 still uses X11

You have some error with Jira. I can't attach an image. I'll try posting the ticket without it and add it later.