But the teams that hire either Flutter or RN tend to not appreciate front end as much. I've been pressured to pick up RN for a while but it turns up negative.
React is a safe framework to pick up. If you're worried about employment, go for it.
Native Android has very similar functionality to Flutter and I think the Flutter devs are moving to Android. If you know Flutter, you already know Jetpack Compose. Android tends to pay very well because it's more of a niche but it's also rare. Since the Crowdstrike incident, Android has become the default operating system for hardware like car radios, those credit card machines, point of sales.
iOS is also interesting because it's half the market share, pays a little more, and AI just sucks at it. There's a bunch of things in Swift that you can't do with Kotlin. Swift is also something the standard LLMs can't do today so there's some job security. And by the time LLMs catch up to the average iOS dev, you could have the kind of mastery level to keep the job.
It never hurts to have one more tool in your toolbelt. Even if you end up hating React, knowing it will allow you to get jobs that currently use it and then you'll have the vocabulary and insider understanding that will allow you to advocate for a different framework or language if you strongly prefer it.
For what it's worth, I see more and more people tiring of Next.js and considering much simpler solutions like Astro, with or without React.
You should learn React. Everyone (including non-web devs) should probably have a basic understanding of React state management. Back in the day when JQuery was the top library, everyone was free to use whatever lib they wanted (and things besides jQuery were better for certain things), but it was also somewhat expected that everyone would have some experience, even in passing, of jQuery.
I do feel flutter delivers more on the one codebase and relative simplicity technology than most things I've tried.
It would remain my first choice if I was starting, and I'd hire non Flutter devs for it.