As you probably already know, Centreon 21.10 is not a supported version anymore (more information here).
As a consequence, the RPM package repository for this version has been archived: it moved from https://packages.centreon.com/rpm-standard/21.10 to https://archives.centreon.com/standard/21.10.
If your platform is still running 21.10 and you need to update it, please update your YUM or DNF repository configuration to handle this change.