Don't know if it's a problem with Normal Opera browser but I'm facing this problem with Opera GX. After I change the default mic. for the browser in the browser setting it's showing the changed mic. as selected Microphone but actually it's not getting changed for those websites where we don't get an option to select audio device (for example https://web.whatsapp.com).
After I give mic. permission to these site(s) it's using the same mic. as default audio device as it was using before I changed the default device.
To verify I ran this method in the console navigator.mediaDevices.enumerateDevices();
And in the [[PromiseResult]] array of the Promise object returned is showing all the devices the page has permission and over there too the deviceId is set to "default" for the wrong device, not the device I selected in the browser settings.
I tried clearing caches and resetting permission for the site but nothing worked.