SDL_GetPrimaryDisplay - Return the primary display.

       This function is available since SDL 3.2.0.

       SDL_GetPrimaryDisplay - Return the primary display.

       Returns  the  instance ID of the primary display on success or 0 on failure; call SDL_GetError() for more
       information.

SDL_GetDisplays(3)

Simple Directmedia Layer                           SDL 3.2.20                           SDL_GetPrimaryDisplay(3)

#include<SDL3/SDL_video.h>SDL_DisplayIDSDL_GetPrimaryDisplay(void);

       This function should only be called on the main thread.