How to ADD multiple URLs in Sitemap?

Dear RankMath Team,

I would like to add some additional URLs in my site > https://www.searchengineradar.com/ and below are the examples of what I want to do:

If you see > https://www.searchenginejournal.com/sitemap_index.xml
you will see there are multiple URLs in sitemap except https://www.searchenginejournal.com/post-sitemap1.xml | https://www.searchenginejournal.com/page-sitemap.xml

And, I want to create exactly same SEJ sitemmap URL like: https://www.searchenginejournal.com/ecommerce-guide-sitemap.xml and then add my other related topics/posts in it for example:https://www.searchenginejournal.com/ecommerce-guide/technical-seo

If I understand correctly they have created a hub page (mother page) for E-Commerce Guide and added Technical SEO page as Child page.

Currently, my website’s sitemap is showing pages https://www.searchengineradar.com/sitemap_index.xml and will show post later.

But again, How can add above SEJ type URLs in my website’s sitemap and how this will work to navigate my pages or post to store in them only.

Please help!

Thank you.
Deepak Sharma