Man pages matching name set_blender_mode_ex in section 3alleg4:

set_blender_mode_ex.3alleg4.en	debian 10 / allegro4-doc
set_blender_mode_ex.3alleg4.en	debian 11 / allegro4-doc
set_blender_mode_ex.3alleg4.en	debian 12 / allegro4-doc