iOS 14 - go to Settings > Affinity Photo. You’ll see the Photos app listed (I did).
It said “selected" next to Photos (meaning Af Photo only has access to ‘selected photos’). Touching that, took me to other options, including “all photos" = job done ✅ .
Each time you update your iOS, I think this might need re-establishing. Or at least a major update (13 to 14). That’s what happened to me. I accidentally ended up with "selected photos only" in the settings after updating my iOS. That, or I did something, which is possible.
