Does anyone know what to do when PyCharm loads, is visible in TaskManager, but there is no window?

I have an issue with PyCharm not starting properly.
No matter, how I open it, even as Admin:
start from exe

It shows the loading screen for a couple of seconds: loading screen

The icon in the taskbar flashes for a second, indicates an open window, but a window never opens. Or maybe it disappears again so quickly?

PyCharm is visible in TaskManger:
PyCharm in TaskManager

And afterwards just sits idle:
PyCharm in TaskManager idle

This issue suddenly started happening yesterday with the previous up-to-date installed version of PyCharm Professional.
I then uninstalled it and installed the newest version.
This is now PyCharm Professional 2021.1 – and the issue still persists.

I have no clue what to do about it, or where to look, since it is apparently running.

Best regards, and thank you.