From zdnet.com:
Meta could be analyzing and retaining photos from your phone’s camera roll — even ones you haven’t uploaded to Facebook — through a controversial feature now available to all Facebook users in the US and Canada, if they choose to opt in.
If you see a “cloud processing” pop-up on Facebook and tap Allow, you’re agreeing to Meta’s AI Terms of Service and permitting your “media and facial features” to be analyzed by Meta’s AI. Once enabled, Facebook continuously uploads photos from your camera roll to Meta’s cloud to surface “hidden gems” and suggest creative edits or collages.