Man pages matching name sdl_wm_setcaption in section 3:

SDL_WM_SetCaption.3.en	debian 10 / libsdl1.2-dev
SDL_WM_SetCaption.3.en	debian 11 / libsdl1.2-dev
SDL_WM_SetCaption.3.en	debian 12 / libsdl1.2-dev