It depends on your exact requirements. If it's something crud based go with an established framework like Django or Rails. Both of these have mature communities

It depends on your exact requirements. If it's something crud based go with an established framework like Django or Rails. Both of these have mature communities, ample tooling, and aren't going anywhere soon. If you're looking to simplify as much as possible from your own perspective, consider using something like Next.js so you only have to learn one language. But you'll have to make other choices, so it's a trade off. I wouldn't go 2 native clients on mobile, but perhaps ionic framework instead.