Note that there is a possibility this may not be intentional, but rather as a short term consequence of having to allow other browsers. The device prompting the user to specify which browser they want to use is evidence of this.
Likely, Apple will fix this later. I simply cannot see them intentionally pulling something like this while the EU is breathing down their necks, and if the change were intentional, it would have been a global change.
This is part of the compliance with "opening in your default browser" if the web site isn't specifically marked as a PWA then it just opens in the default browser. If it has a PWA manifest then it opens as a app using of course on Webkit as the rendering engine.
Likely, Apple will fix this later. I simply cannot see them intentionally pulling something like this while the EU is breathing down their necks, and if the change were intentional, it would have been a global change.