Expanded Controller Support
This has to be my most frustrating portion of iOS, especially iPadOS.
None of the standard games I play (and my iPad Mini is dedicated fully to mobile gaming) support an external controller. These are games that involve active movement such as Dragalia Lost and Genshin Impact, and in the case of the latter already supports it on consoles and PC.
Apple needs to push the controller API harder on these developers to get them to integrate it. I know the Apple Arcade has a requirement for it of some sort, but it would be nice if Apple's API teams really nag this support for "active" controls (i.e. not tap-controlled interfaces) in all games. I find touchscreen controls, especially virtual "analog sticks", on these games frustrating and tend to avoid using the mobile version of them for this exact and specific reason.