Man pages matching name al_unmap_rgb_f in section 3alleg5:

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