robots.txt and sitemap.xml for a new site
robots.txt
Put this at https://yoursite.com/robots.txt:
User-agent: *
Allow: /
Sitemap: https://yoursite.com/sitemap.xml
Watch out for Disallow: / under User-agent: *. That blocks all search engines and often gets left over from staging. Also check for <meta name="robots" content="noindex"> in your page head.
sitemap.xml
<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<url><loc>https://yoursite.com/</loc></url>
<url><loc>https://yoursite.com/pricing</loc></url>
</urlset>
List every public page. Next.js can generate this for you with an app/sitemap.js file.
Submit it
Add your site to Google Search Console, verify it, and submit the sitemap URL. Bing Webmaster Tools can import from Search Console.