Most would call it a bug. I suspect, behind closed doors, Facebook secretly calls it a feature. Facebook has yet to post an official response.
And it seems to be down to how the Facebook app handles access to iPhone and iPad cameras in the latest version of iOS 13. To squash the bug for the time being, iPhone and iPad users can simply remove the Facebook app’s camera access in the device settings, or just purge the app from their iGadgets completely.
If you’re into conspiracy theories, you might argue that this was a deliberate move by Facebook to gobble up more user data. And we’d not blame you given the data handling mess that came to light last year with the Cambridge Analytica data-sharing scandal, as well as other borks by Facebook in keeping its user data private.