There is a server protection module that prevents accessing your staging site directly so I'm not able to check the sitemap on your staging site. However, I do not see that on your live site.
On the staging site, please try to clear some caches: plugin, browser, hosting ... and disable/enable the sitemap option to see if it works.
If not, I would like to request temporary access (wp-admin and FTP) to your staging site to take a better look at the issue. Your next reply is set to private to share the info.
❌ IMPORTANT: Please backup your database and website before proceeding ❌
You can use this plugin to create the backup: https://wordpress.org/plugins/duplicator/
✙ I would need your permission to de-activate and re-activate Plugins and the Theme to change configurations on the site if needed. This is also a reason the backup is critical.