We know that microphone use on iPhone requires an entitlement and if an app is actively using audio in the background, an indicator appears on the screen. This has been true for ages.

I assume Android has something similar to this but I’m not in touch with the Android ecosystem. This article is pretty old so I can believe that apps, far enough in the past, could do this. But it is otherwise some fearmongering you would see copy-pasted among tech illiterate.