In iOS 18.2, Apple introduced a Categories feature to the Mail app, which automatically sorts emails into four sections: Primary, Transactions, Updates, and Promotions.
While Categories aims to help manage email overload, not everyone will prefer the new layout.
If you want to switch back to the traditional list view in Apple Mail, you can do so easily by selecting List View from the pop-up menu on iPhone/iPad or unchecking 'Show Mail Categories' on Mac.
You can always switch back to Categories view using the same menu if you want to try it again later.