Your sitemap.xml actually only contains the address for sitemap0.xml
but the real sitemap is on that file that contains 0 in the name.
HTTP vs HTTPS also
in most cases, it is normal for Google to report that error at the beginning,
sometimes depends on DNS propagation, but mostly on the GSC system itself.
If you really insist, you can edit the cache time for xml files via .htaccess
# Prevent caching of XML files
<FilesMatch "\.(xml)$">
Header set Cache-Control "max-age=0, private, no-store, no-cache, must-revalidate"
</FilesMatch>