Prior to iOS 26, it was possible to design an inputAccessoryView(Controller) that would integrate seamlessly with the system keyboard, by which I mean appearing as a natural extension of the system keyboard. For example, using CYRKeyboardButton <https://github.com/tmcintos/CYRKeyboardButton>.
To date, I have successfully used this to provide an enhanced numeric key row within my apps, which is a distinguishing feature of these apps. It took a lot of engineering and testing effort to perfect this design. However, with iOS 26 the design is completely broken due to the system keyboard UI change, which makes it impossible to display an inputAccessoryView seamlessly along the top of the system keyboard (see attached screenshots).
In my opinion, it is just plain reckless for Apple to make these kinds of trivial UI changes, which break existing app designs without adding any significant value to the user experience.
iOS ≤ 18.x:
iOS 26 beta: