Hello,
Thanks for contacting us, and sorry for any inconvenience that might have been caused due to that.
When there are more than 200 posts, another child sitemap should be automatically created for other URLs, and it should be look like /post-sitemap1.xml or /post-sitemap2.xml.
If you can’t see something like I mentioned above, then your sitemap might be heavily cached. Can you please try following the steps below to see if that works for you?
1. Flush the Sitemap cache by following this video screencast:
https://i.rankmath.com/pipRDp
2. Exclude the Sitemap files of the Rank Math plugin in your caching plugin. The cache could be via a plugin or from the server. For plugins or Cloudflare, please follow this article:
https://rankmath.com/kb/exclude-sitemaps-from-caching/
3. If the above steps doesn’t seem to work, kindly apply the following filter code to your site.
add_filter( 'rank_math/sitemap/enable_caching', '__return_false');
Here’s how you can add filter/hook to your WordPress site:
https://rankmath.com/kb/wordpress-hooks-actions-filters/
If the issue persists, share your sitemap URL with us here. So that we can check as well.
Let us know how it goes. Looking forward to helping you.
Thank you.
Here is my sitemap link: https://exactgayceleb.com/sitemap_index.xml
please check this and let me know why a child sitemap didn’t create automatically after reaching the 200 post URL.
Thanks
One more thing i have to tell you, in my RankMath plugin if i visit Sitemap Setting> General > i only see two options are available 1. Images in Sitemaps 2. Include Featured Images
These two options only. In General settings, i didn’t find any options like Like Per Sitemap and Ping Search Engines.
Why my General Settings dashboard show incomplete? 
Hello,
Please note that some options are only available when you enable the Advanced Mode in Rank Math. If the Links Per Sitemap and Ping Search Engines options are not showing on your Sitemap Settings, you must have chosen to use the Easy Mode. Please try to switch in Advance mode from Rank Math > Dashboard.

That should reveal the options on your Sitemap Settings.
You can follow this URL for more details on Advanced Mode:
https://rankmath.com/kb/advanced-mode/
Hope that helps. Please don’t hesitate to let us know if you have any other questions.
Thank you.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.