My iPhone 16 camera has been shuttering

That’s normal. When you get to within about 8” to a subject, iPhone automatically switches from 24mm 1X lens to 13mm .5X lens. The 13mm lens is required for macro or closeup photography.

There is a setting within Camera settings to enable the Macro Control.

Yes, because you’re at the distance where it switches between lenses. Either move the camera closer or further away and it will stop switching.

That’s the only thing left. Contact Apple Support and have them diagnose the issue. Your iPhone 16 is still under warranty.

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What model iPhone does your colleague have macro is different on iPhone 16 models.