I would check at the URLs opera://settings/content/camera and opera://settings/content/microphone to make sure there's nothing in the allow list that you don't want to be there.
Also, disable your extensions one by one at the URL opera://extensions to see if one is the culprit.
Also, for each sidebar app you use, click the lock icon at the top middle of the panel and goto site settings and review the camera and microphone settings there too.
You can see if it happens in a test standalone installation of Opera too or not. That'll tell you if it's just your Opera's settings or something that's messed up.