I'd focus on what platform you like working in. As a backend dev that has built a few mobile apps in Android and iOS, I hated wait for code to build and deploy

I'd focus on what platform you like working in. As a backend dev that has built a few mobile apps in Android and iOS, I hated wait for code to build and deploy to mobile phones. I hated trying to track down errors that only happen on certain devices or tweaking the UI for each phone screen. I hated the annual upgrade monkey dance to support the new version of iOS or Android. If you switch languages or platforms, you may take a pay hit while you ramp up or you might can get lucky and find a company that will pay full price you to learn the tooling. Typically, there will be an opportunity cost of learning swift instead of getting paid to do what you know. If it takes 200 hours of learning and you earn $50/hr, that will set you back $10k in lost time. Don't change because of money. Change because you're bored of react.