Oh, interesting. I removed the WIN32 option in CMake's ADD_EXECUTABLE and this created the project with SubSystem CONSOLE. When the application is launched, this opens a Console window, and immediately after my Qt ui

I don't want to have a console in the background that can be closed by mistake and kills the main Qt application, but this gives me new things to investigate. For starters I found this:

https://www.devever.net/~hl/win32con

Thank you all for your help!