As I noticed now, audio recording seems to be completley disabled since the Android 10 update. The only thing still working seems to be audio in phonecalls. But the sound in recorded videos is silent, and several audio recording apps don’t work anymore. I’ve heard of a new “security feature” in Android 10 or another way audio recording is handeled, but this looks like a real bug to me.
It used to work fine in Android 9, and the microphone persmissions are set. I’ve already sent a bug report to the support.