In my case, using Windows 10 and with the Hero 9 updated to the latest firmware, the software worked fine for the first use but then stopped working subsequently.
In fact, every time I plug it in Windows notification tells me that there is a Camera Connection Error and to try and reconnect the camera.
Of course this produces no different results, always the error.
At first, after doing some research, where I found many with the same problem, I decided to uninstall and reinstall the GoPro Webcam software.
That solved nothing of course, I'm not a big fan of uninstalling and reinstalling software as it rarely cures any problems.
Interestingly though the uninstaller wanted me to remove Microsoft's News Suite. Not a problem, as that is something I never use.
So what do I do now?
Well, this is my workaround; until some kind of fix is issued as it is definitely a software bug - edit: it's still a problem but this method works.