"Demo" inaccessible on https://demo.owncloud.org/

When I click on the "Demo" button in https://owncloud.org/ my browser Firefox says :
"demo.owncloud.org uses an invalid security certificate.
The certificate is valid only for the following names: owncloud.org , www.owncloud.org

-> I can not identify on the website an email contact to report the problem.

True. We are working on a new demo system. We should leave a message there explaining the service is unavailable at the moment.

ref https://github.com/owncloud/core/issues/26921