We get this question on probably half our mobile project intakes. There is no universal answer, but here is the framework we use.
Pick React Native when: the client already has a React-heavy web team, the team values fast iteration over peak performance, or you are building a content-driven, commerce, or social-style app where 60fps animations are not life-or-death.
Pick Flutter when: the UI is the product (custom design language, lots of motion, brand-distinctive components), or you want closer-to-native performance for graphics-heavy screens. Also: when you do not have a web team to share code with.
Both ecosystems are mature enough now that the “which is more capable” debate is over. They are both capable. The question is which fits your team and your product.
One thing we will not recommend either of for: real-time camera, AR, or heavy on-device ML. Go native. The bridges are not worth it.