Run the check
Open the webcam test and note the exact permission or device error before changing settings.
Close other camera applications completely, then retry with the same camera selected in the browser.
If it still fails, test the camera in the operating system's camera app and compare another browser.
Read the result
A preview that starts after another app releases the camera supports an occupancy conflict. A permission-denied message needs the separate camera-permission guide. A frozen active preview needs a stream check.
Limits and next step
Browsers do not reliably name the other process using a camera, and some devices permit concurrent streams while others do not.
Repeat the check after changing one setting or connection. Keep a record of what changed before deciding whether the device needs service.