This is not evidence that they’re using your microphone, and you know it’s not.

I didn't claim it to be evidence for that.

somehow bypassing Google and Apple’s mic usage notifications

Unless some form of hardware notification is hardwired into the device, which indicates cam or mic usage, I'm on the rather paranoid side regarding software notifications. Software is usually much easier to break. I'm leaning a lot out of the window now, as I don't know how secure those notifications are implemented. However, even then there is reason for concern, given that facebook had / has questionable deals with device manufacturers. If they were willing to share personal data with device manufacturers, there is reason to suspect this went or can go the other way around as well.

I don’t know why you keep coming back to trust. [...] That’s not the point.

It is mine. Even though there is no evidence for a surveillance using device microphones itself yet and it could be surprising if they were able to, given the history of facebook, they participated in a lot of rather surprising shit.