Depends on the app I guess, but you can get far without needing a Mac with flutter etc. Sadly I think there still is some restrictions for some Apple hardware for the developer part of the app store. I'm not super familiar with that part, but we had some issues with some Apple legal terms which could only be accepted on a authenticated device, which means you need Apple hardware.
Whatever solution you pick for iOS dev: Flutter, React Native, Xamarin etc etc, in the end we will always meet the same thing: iOS SDK. And iOS SDK only runs on Mac, unlike Android.
Unless Apple decide to port their SDK to Windows/Linux (which I believe will not happen), you can't practically avoid Mac.
