Everything you need to learn about native iOS and Android is already provided by Alex and Rahul.\
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I'll give you my perspective as a Tech lead in one of the Big Tech companies. I have been doing Android for over 10 years and roughly 6 years ago, I was exposed to [React Native](https://reactnative.dev/). I hated Javascript before learning React. My mentor advised to me have a diverse perspective and look at each framework as a tool to get my job done.\
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I learned React native - became an expert at my company eventually. After moving into Big Tech, that skill of building product on both platforms helped me greatly. I would also encourage to get your native app fundamentals right on at least one platform before trying cross platform work.

Software Engineer @ Amazon

Bala Ram

Adding to what Rahul and David suggested:

It's also good to have a business impact added to the problems/projects you worked on. A problem may be complex but its real value is tied to your business. By talking about how you approached and prioritized the problems to serve the best value for your business a good skill to demonstrate.