From an article about a recent lawsuit

The App Store appeared to harvest information about every single thing you did in real time, including what you tapped on, which apps you search for, what ads you saw, and how long you looked at a given app and how you found it. The app sent details about you and your device as well, including ID numbers, what kind of phone you’re using, your screen resolution, your keyboard languages, how you’re connected to the internet—notably, the kind of information commonly used for device fingerprinting.

Notably, knowing keyboard language and monitoring tap locations allows for reconstruction of text the user types (as detailed in this article

I do think you are correct that Apple probably isn't actively keylogging every iOS device (just because there's easier ways with less legal concerns that ultimately get the same outcomes), but it's not like there's "no evidence".