My answer will be little subjective because I am a React Developer for some time now. It all depends on how much time and effort you want to put in to start with. If you want to learn basic concepts quick then start working on improving your skills I would say start with React. ( assuming you have some JS experience) then move on to React Native. React, as a UI library, has shallow learning curve and concepts are pretty straight-forward. It comes with the fundamental core library and you take it from there with your own components or shared modules.
If you have plenty of time and want to learn everybody is so adamant about, go with Angular. I have barely have any experience with Angular so I can really talk about it, won't be fair, but as far as I know, it is a framework and comes with all the tools you need. It is pretty opinionated so you have to go with what they gave you. And over the years it got so complex that learning curve is pretty steep.