When I start Steam, my cursor moves to the upper left corner and it is stuck there. What can I do against it?

When I start Steam my cursor moves to the upper left corner and it hangs there also pops up a small info window in the lower left, saying that my Nintendo Switch Pro Controller needs the controller configuration (or something like that), although I haven't even switched it on have or is not even (not at the moment) connected to the PC.

I have no experience with the problem, so I can only guess at first. You could try deactivating the "Switch Pro Configuration Assistant" under Settings. This may solve your problem.

Steam should then no longer try to use the Pro Controller.