Man pages matching name al_have_opengl_extension in section 3alleg5:

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