What was Apple's Project Michigan

It was Apple's internal codename for its compliance efforts relating to the Epic Games v. Apple court injunction. So this was about allowing purchase links in apps. The drama is that they put this big warning screen up:

You're about to leave the app and go to an external website. Apple is not responsible for the privacy or security of purchases made on the web.

Sources: Epic Games v. Apple Order Enforcing Injunction, Tim Sweeney tweet