According to an earlier reliable Weibo account, the iPhone 16 will get an additional button. This so-called Capture Button will be placed right below the power button and serve as a shutter button. Currently, mainly Sony uses a physical shutter button on their Xperia phones.
The Capture Button should end up in approximately the exact spot where the mmWave antenna sits on American models. On European models, this spot is empty. The additional button will be a capacitive one, like the recently introduced Action Button, which means that the button registers more than touch.
The Capture Button on the Apple iPhone 16 can be used by the camera as a shutter button. And because it is capacitive, it also responds to swiping. Exactly what functionality Apple gives it remains to be seen. Rarely do cell phones have a separate shutter button, despite being very useful for capturing photos. However, pressing a volume button usually has the same result. Sony is the exception to the rule; most Xperia phones have a dedicated shutter button.
Not yet a solid-state button
Earlier still, it was rumored that Apple wanted to transition from physical buttons to solid-state buttons. These kinds are not pushable buttons but behave that way thanks to a vibration motor. That rumor hasn't come true yet; for example, the volume and power buttons are still physical. And even on the iPhone 16, that will most likely remain the case.