Can the middle screen be upgraded to an apple screen, like an add on?
Ask your dealer to know for sure… but I seriously doubt it.
The technology you want is called Apple CarPlay. It is not available for the '17 Forester. The Forester was updated for 2019 and the technology is now available in that model year vehicle.
Your best bet is to go with an aftermarket head unit from someplace like Crutchfield. It won’t be cheap, though.