Missing sitemap.xml reference inquiry

Hi all,

Super SEO newb here, looking for some insight into sitemaps, robots.txt files, and Google Search Console.

My site auditor tool is reporting "Missing Sitemap.xml Reference" as a warning for a client's website. I have a basic understanding of sitemaps, but here's my question:

Is it best practice to include the sitemap in a robots.txt file and to submit the sitemap to Search Console manually? Or am I just being redundant at this point?

If you have any good resources I'd love to learn more!