Man pages matching name flex in section 1:

flex.1.en	debian 10 / flex
flex.1.en	debian 10 / flex-old
flex.1.es	debian 10 / manpages-es-extra
flex.1.ja	debian 10 / manpages-ja
flex.1.pl	debian 10 / manpages-pl
flex.1.en	debian 11 / flex
flex.1.en	debian 11 / flex-old
flex.1.ja	debian 11 / manpages-ja
flex.1.pl	debian 11 / manpages-pl
flex.1.en	debian 12 / flex
flex.1.en	debian 12 / flex-old
flex.1.da	debian 12 / manpages-da
flex.1.ja	debian 12 / manpages-ja
flex.1.pl	debian 12 / manpages-pl
flex.1.ro	debian 12 / manpages-ro
flex.1.sr	debian 12 / manpages-sr
flex.1.sv	debian 12 / manpages-sv
flex.1.vi	debian 12 / manpages-vi