Under Preferences > Media Settings there is no Video Device detected although I have a webcam and any other application on the desktop can work with it without a problem.
Well. There is no video chat support in Spark. So you are not missing out on anything. Voice chat is broken currently also. I guess maybe this field was introduced for some video chat plugin which is not available anymore.
I believe so. There was the Redfire plugin many years ago, which if i remember correctly had video chat support. But it is not compatible and not developed for a long time (maybe old versions will work with Spark 2.6 or older, but not with Spark 2.7.x). Voice chat is broken for some time and as nobody is working on it right now, can’t even tell when it would be fixed. Stun settings are for the voice chat.