How to send data from a React form to a php page and redirect the user to the same page?

Question

React

I have a form on Next.js, when filled, the function of sending data via fetch is executed.
If I don’t specify event.preventDefault() in the function, then I get something completely different (I don’t even know how to describe it).
I just hope that someone has already encountered such a situation and will be able to correctly describe it, and show an example of a solution.