Routing problems with MERN stack app

I am having routing problems with this project.

The new registration page (React) works (created a new user) but I can’t redirect to another page.

I have another registration page which does work that uses express-handlebars but I want to replace that eventually.

I am also having problems with validation. The form still submits even with errors.
What’s the best strategy here? Disable the submit button until a form is valid?