I'd expand on one of your best skills you already have. The "stack" gets more and more complicated so "full stack" will stop to be a thing in the future.

If you are already good in react, learn more libraries / frameworks in that ecosystem and increase your day rate. You are a frontend architect now.

I'd start with things like nextjs, Gatsby or Redux saga.

You could also go into the devops side of Frontend. Learn the different approaches of deploying / scaling a Frontend with server-side rendering (vercel, digital Ocean, docker...)