You should buy a domain that matches your company, your publisher name, or albeit your own personal site as long as it matches the publisher details on the extension page.

Then you will need to create and host both Terms of Service and Privacy Policy on those pages. This will get you approved.

I am not sure but you could be able to get by with something like Netlify Pages where you get a subdomain under their domain. However that is a pure guess.

A good rule of thumb is to verify the domain using Google Search Console (this is a prerequisite) and then pick as the official domain for the extension. This will get you there. This will also speed up your reviews down the road by a margin.