A major thing that iOS doesn't have and even iPadOS 12 didn't is the ability to do a side-by-side view of two windows of the same app (two Mail windows, two Safari, two Pages, etc). Sounds pretty basic, but previously the split-screen view had to be two different apps.

That requires app opt-in: it's not automatically enabled (your apps will need to update for this to work).

iOS 12 does side by side web pages.

If folding devices become a trend, there will be less need for convergence then? :)