iOS does not exist as a platform I can choose anywhere in 10.3. Even if it did exist, AFAIK I would still be required to choose an SDK before I could add iOS as a target platform in a project. But I cannot add any iOS SDK at all, as described in my question.
Edit: and when I want to add a SDK, I have to choose the platform before I can choose what Connection Profile I want, which leads me to conclude that it has nothing to do with XCode because it doesn't even connect with XCode to check, but maybe the macOS build caused the iOS platform to be removed?
Edit2: I tried to build and run an empty iOS app with XCode, then building and running a macOS app with Delphi, but still no change.