Many components in an iPhone are paired to the logic board from the factory, so if they need to be replaced you have no choice but to go down the Apple sanctioned repair path (although the third party industry goes to great lengths to work around it). Some components, like the display, will show a warning notification in iOS for weeks and disable features like True Tone and auto-brightness if swapped with a third party part. Other components such as the cameras can't even be swapped between 100% genuine iPhones.

https://www.ifixit.com/News/82867/iphone-15-teardown-reveals...

The iPhone 6 disabled Touch ID when the home button was replaced but it'd still function fine as a button - until you restored the phone, which would fall over with an arbitrary error code forcing you to take the phone in to Apple for repair. There was a lot of backlash before they caved and fixed the update process: https://www.theguardian.com/money/2016/feb/05/error-53-apple...

Look up Lewis Rossman, he runs a repair shop and complains all the time about this