at the site https://www.mediawiki.org/xml/ the entry export-0.11 is missing.
But apparently the page is there https://www.mediawiki.org/xml/export-0.11/
Change 710011 had a related patch set uploaded (by Reedy; author: Reedy):
[operations/mediawiki-config@master] Add export-0.11 to xml/index.html
Change 710011 merged by jenkins-bot:
Mentioned in SAL (#wikimedia-operations) [2021-08-04T11:53:47Z] <reedy@deploy1002> Synchronized docroot/mediawiki.org/xml/index.html: T288040 (duration: 01m 08s)
Done. If it's not showing now, it's probably due to caching.
Pages purged and seen working from here at least