It depends on what you want to build. If you are accessing the common features across platforms (iOS and Android), then you may likely find support on cross platform solutions like React Native, Ionic etc.
I always prefer maintaining two separate stacks unless it's an easier app to build.
React Native is being adopted at rapid pace and the community is also vibrant. There are still some rough edges if your application needs to access exclusive features of a platform or something not very common (for e.g. many third-party services doesn't offer a cross platform SDK like ReactNative, they usually have the ones for iOS and Android). This imposes restrictions in using React native and you may end up writing platform specific code separately. Good thing with React is that, you can partially use React within in your existing project. You are in control.
Decide what to do next, then look support under each platform/framework to build things you want.