I think if you have a good understanding of the DOM and you’re comfortable building things in vanilla JS you’ll be fine to move on to React. Especially if you’ve already built sites and web apps with JS or a JS templating engine like EJS, Handlebars or something you’ll be ready for sure.
I think that once you’ve learned the basics on DOM manipulation, it’s time to move on. Most jobs will expect some kind of f/e view interface library like React, Angular, or Vue. There are also some that use SSR like EJS, etc. I personally think think that f/e libraries are the future, but I don’t have stats to back that up. FCC teaches React - that’s a good library with a bright future.
Be careful about the “I don’t want to move on until l master this” philosophy. While it may seem commendable, in programming it can be crippling. There will be many times when you just need to get to the “I kind of understand this but I’m going to keep moving forward and I can circle back to this if I need to” state.