Man pages matching name allegro_prim_buffer_flags in section 3alleg5:

ALLEGRO_PRIM_BUFFER_FLAGS.3alleg5.en	debian 10 / allegro5-doc
ALLEGRO_PRIM_BUFFER_FLAGS.3alleg5.en	debian 11 / allegro5-doc
ALLEGRO_PRIM_BUFFER_FLAGS.3alleg5.en	debian 12 / allegro5-doc