Hello,
Thanks for contacting us and sorry for any inconvenience that might have been caused due to that.
I can check that your sitemap only has page sitemap inside it:

Please check and let us know if you need any other assistance.
https://nacht-depesche.de/sitemap_index.xml —here is my sitemap, sorry for the inconvenience
Hello,
For initial troubleshooting, please follow these steps:
1. Ensure you’re using the latest version of your plugins/theme including the Rank Math plugin.
2. Flush the Sitemap cache by following this video screencast:
https://i.rankmath.com/xXXhDt
3. Exclude the Sitemap files of the Rank Math plugin in your caching plugin. The cache could be via a plugin or from the server:
https://rankmath.com/kb/exclude-sitemaps-from-caching/
If the issue still persists, please check if this option is enabled in Rank Math > Sitemap Settings > Jet Engine post type

I hope that helps.
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.