The Reddit iOS app and mobile redesign are improvements from past UX. In app media seems to also be better than the past link outs. And the ads have overall gotten better and less intrusive feeling.
Getting a popup, sometimes undismissable, to read the thread in the mobile app (with no option for alternatives) is the opposite of what I would call an “improvement”, even if the before is old.reddit on mobile (ignoring mobile specific sites like i.reddit et al).
There is no “past UX” for the iOS app. If anything, it’s a downgrade of Alien Blue, the 3rd party app they bought out then neutered.
Making the experience worse for mobile users for the sake of tracking engagement is certainly not “nothing”, you’re right about that. It’s worse than nothing.
I wouldn’t call all that “nothing”