I think you should chose between Flutter and Ionic. With those two options, the main question is about graphs and performance. Are they really important for your application? If the answer is yes, your tool is Flutter but, if the answer is that you need an easy tool to create an app with some basic components I would choose Ionic. You have a library with lots of components that you can use and they have native UI by default (for Android and iOS).

You will find more support if you use Ionic with Angular as frontend framework (you have the option to use Vue or React but this is a new feature for Ionic and I think there are more difficult to learn than Angular).

You can develop and debug the majority of features on PC (I don't know if that is possible with Flutter). And when you will finish the app, create iOS and Android versions is simple.