How do we, as a whole team, level up? Do other companies provide coaching or other resources?
I'd start with that. Have a conversation with the whole team and get a feel for if they agree with your assessment that the React code is amateurish and the team doesn't fully understand it. BE CAREFUL how you approach this conversation. It really sounds like it is your personal opinion that the codebase is amateurish. If others don't agree, you can really damage your professional relationships on the team if you aren't gentle with your criticism here.
If the team is not in agreement, then it probably ends there. Pushing it further will only cause problems for you in this case.
If the team does agree that everyone needs to skill up, then you will collectively need to agree on what areas to work on. I'd suggest the team find a good online course and everyone complete it. That's a good starting point, making sure everyone has the same baseline understanding of the technology.
Past that, if the team can hire a good experienced developer in the technology to act as a mentor that's always a good person to have around.
All of this advice is based around answering the question you asked, but I would also like to encourage you to re-frame your thinking. Instead of thinking that the team needs to skill up and approaching it like that is the problem to solve, I recommend approaching it as a personal improvement project.
Work on your own skills with React, take courses, look at other examples of codebases that do it well. Start to implement what you learn into your own work. Do refactors in the areas of the code you work in. Make suggestions for improvments on coworkers PRs. In short: Seek to become the mentor you think your team needs in order to improve, and lead by example.