Hello,
Thanks for contacting us and sorry for any inconvenience that might have been caused due to that.
I can check that all the versions of your sitemap are returning a 200 status except the https://www version.

Please ensure that only 1 version of the sitemap is working (200 status), and the rest are redirecting to it. You can also use this tool to check. Please follow the steps in this link:
https://rankmath.com/kb/couldnt-fetch-error-google-search-console/#5-check-for-the-correct-version-of-the-sitemap and redirect the WWW version to the non-WWW version.
Once done, resubmit the correct version of your sitemap_index.xml in the Search Console.
Let us know how that goes. Looking forward to helping you.
Thanks.
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.