Man pages matching name datetime::format::w3cdtf in section 3pm:

DateTime::Format::W3CDTF.3pm.en	debian 10 / libdatetime-format-w3cdtf-perl
DateTime::Format::W3CDTF.3pm.en	debian 11 / libdatetime-format-w3cdtf-perl
DateTime::Format::W3CDTF.3pm.en	debian 12 / libdatetime-format-w3cdtf-perl