Man pages matching name datetime::format::rfc3339 in section 3pm:

DateTime::Format::RFC3339.3pm.en	debian 10 / libdatetime-format-rfc3339-perl
DateTime::Format::RFC3339.3pm.en	debian 11 / libdatetime-format-rfc3339-perl
DateTime::Format::RFC3339.3pm.en	debian 12 / libdatetime-format-rfc3339-perl