This question came up last game. Thanks in advance for any input because I couldn’t find anything on it.
In the gamemastering chapter in bold print it says a player can not have more than 5.
A direct quote to specify the RAW on fortune:
“Each player character usually begins each session
with three Fortune points (though some characters may
begin each session with fewer), and cannot have more
than five Fortune points at any time. Any excess points
are immediately discarded, rather than being spent.”