Man pages matching name al_toggle_menu_item_flags in section 3alleg5:

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