Viewer? Probably just Quick Look. It's built into the Files app.

If you want to edit, just use Apple Photos. Everything is in there anyway.

Huh? Are there other gallery apps to iOS other than Apple's app? /s

If you want to choose between multiple gallery apps, Android would probably be your best choice. Fossify Gallery is the best one if you ask me.

Plus, any device from Apple is not a good privacy choice. Just saying. You are the product - literally. You don't even own the devices even if you buy them! Apple has that much control over you!

Update: I checked the App Store on my "I want to learn the system" iPhone that I got for free. I did found numerous gallery apps, but none with as good privacy features as what Fossify Gallery have.

The one built into the OS. You shouldn't trust another app with full photo access.

Ente photos