Maybe : Appgyver could work for the app part. Have not had time to try it out myself, but I think you are able to get react native code from the build.
Wappler will give you a good backend. Like a proper backend. A whole lot more powerful and flexible than bubble. In a while Wappler will probably have stepped up it’s game regarding apps too 
Example of AppGyver using bubble as a backend : https://seanhoots22.gitbook.io/tutorials/appgyver-3rd-party-authentication-with-bubble
But you will probably not regret using Wappler for the backend