Apple added an App Store rule specifically to prohibit this, see the first FAQ at https://developer.apple.com/app-store/user-privacy-and-data-...

It is okay for games to have limited gameplay until you use in-app purchases to unlock more features. You could easily have an app that provides a limited bit of functionality, but then allow you to unlock more just by changing this setting. Especially if any of the monopoly cases against Apple forces them to change.

The proper way of handling that would be to show less ads to those who enabled tracking.

Tracked ads have more value because it's more likely that you'll buy something targeted at you. So you need to show less ads compared to untracked ads to extract the same value.

I think that this kind of differentiation is allowed by Apple and probably will be implemented in some apps.

What about a feature that is both useful and, by its nature, requires tracking to even work? (not a dark pattern but technically depends on something that falls under the purview of tracking)