Depends on what level do you trust. For me, I'd generally trust OS indicators. So, if iOS doesn't show me a mic on indicator when Facebook is not open I'll consider thar verification.

A potentially better option would be if some independent non profit security firm audited major apps every once in a while, monitoring network traffic and such.

"If there was an API for uploading your secret conversations, it would be the holy grail discovery for a security researcher. Someone would have found it."

"That 20 dollar bill lying on the ground in front of me clearly does not exist. Somebody would have picked it up already!"

Yeah the logic here is seriously lacking. Heartbleed shows that it's entirely possible someone might not find it for over a decade! Or the most recent Apple Bootrom exploit.

Or, y'know, the NSO group exploit.

I think the difference here is that apps getting uploaded to the app store have static analysis run on them looking for unauthorized calls. Still doesn't rule it out, but adds an extra check to the process.