This article explains how the macro mode works on the iPhone 13 Pro and Pro Max.

Unless you turn the setting off (see below), the iPhone 13 Pro and Pro Max will automatically switch to macro mode when the phone detects you’re close to an object. So, for example, if you see an interesting flower, open the camera app and move closer to the flower. The phone will detect that you’re close and switch to macro mode. It will return to regular camera mode when you move away.

Some people find the automatic switch to macro mode annoying. That's why iOS introduced a new setting that lets you disable automatic switching to macro mode.

Open the Settings app.