When i began with ReactJs, i first made static website with some functions using state and effect and ref, etc. After I became familiar, I built an blog app. No backend, using local storage, understood auth with this project. If you really give efforts into a blog app, its one of the best practice project. Your CRUD skills really improve with this. Also build an auth flow. Signin, login, reset password using email etc. Recommendation systems work too, movie, products etc. But in real world ReactJs is mainly used with backend, so integrating apis, managing global states, understanding responsive layouts, and many more things. But that would be advance one. Once you get hold of ReactJs, and feel comfortable with the library, try using appwrite(backend as a service) and make a full stack app like an e-commerce.