Please branch and build mailman3 in epel9.
FEDORA-EPEL-2023-f022c8f3ad has been submitted as an update to Fedora EPEL 9. https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2023-f022c8f3ad
FEDORA-EPEL-2023-f022c8f3ad has been pushed to the Fedora EPEL 9 stable repository. If problem still persists, please make note of it in this bug report.