The official FPC 3.0.4 macOS installer installs man pages into /usr/local/man/[man1|man5].
This is incorrect. man does not find them.
They should be installed into /usr/local/share/man/[man1|man5].
[Note: I used the 3.0.4 not 3.0.4a installer because the latter was not available at the time, but I doubt this issue has changed in the a version.]