It’s a button. It serves other functions besides being the home of Touch ID, e.g. invoking Siri, returning to home, etc.
Or are you asking if it’s haptic, like the Apple Watch Digital Crowning?
It has to be a physical button. The Taptic Engine doesn’t work well on bigger form factor. That’s why iPads were rocking physical buttons when iPhones switched to the non moving glass Touch ID buttons.
The power button physically clicks, so it’s not like the home button in the iPhone 7 (and newer). It basically works like the power button on all iPhones.
I think that when you are in doubt, the best way to find out is clicking it when the device is turned off as in my iPhone 7, when the device was turned off, the haptic home button would not “click” since the system was off. ?