This all depends, what you made with Flutter 2 years ago will not build today (so much for easier to maintain). React Native is garbage. There is also Xamarin (terrible, you build a UI for iOS and one for Android). There is Qt as well, a gigantic pain. The best tool I have been able to fulfill the cost-effectiveness, resource efficiency has been Delphi with the Skia4Delphi engine, but it is not roses and butterflies, you need to know what you are doing just as much as with all the other frameworks listed. I have deployed several iOS, Android, MacOS, and Windows apps/tools with Delphi quickly and successfully. I did it with Flutter too, but I was utterly disappointed and Dart was not bad. However, making a MVVM app with Delphi was far faster and cleaner than using bloc with Flutter. I have done native also for both Android (Java/Kotlin) and iOS (only Swift). Native will work, but two code bases can be a pain to maintain, however it works as expected and problems are only specific to the system and independent of each other. If you go native do Kotlin so you can transition to Swift easily.