Hello.
This might be a bit wide topic for this forum, but we have encountered issues with few Android mobile devices and MediaStreams. It seems that both our app that uses openvidu-browser and OpenVidu Call app have similar difficulties getting access to video devices.
At least Samsung A52 and A72 have difficulties giving access to video devices. For example with Call App, it sometimes does not list any devices in session join view. After clearing browser data (Chrome), Call app worked initially but after retries (page close and re-open) it lists all devices correctly, but displays black video element.
In our app, black screen is caused by inactive MediaStream. MediaStream turns to active after one or more navigator.mediaDevices.getUserMedia calls.
As said, this can be complicated topic but if you have any idea what could be the issue, please enlighten us. We would also like to hear if you have encountered anything similar 
BR,
Jere