Man pages matching name rdf::query::algebra::optional in section 3pm:

RDF::Query::Algebra::Optional.3pm.en	debian 10 / librdf-query-perl
RDF::Query::Algebra::Optional.3pm.en	debian 11 / librdf-query-perl
RDF::Query::Algebra::Optional.3pm.en	debian 12 / librdf-query-perl