SDL/android-project/app/jni/src/YourSourceHere.c

#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h>

/* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! */
/*                                                       */
/* Remove this source, and replace with your SDL sources */
/*                                                       */
/* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! */

int main(int argc, char *argv[]) {
    (void)argc;
    (void)argv;
    if (!SDL_Init(SDL_INIT_EVENTS | SDL_INIT_VIDEO)) {
        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "SDL_Init failed (%s)", SDL_GetError());
        return 1;
    }

    if (!SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_INFORMATION, "Hello World",
                                 "!! Your SDL project successfully runs on Android !!", NULL)) {
        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "SDL_ShowSimpleMessageBox failed (%s)", SDL_GetError());
        return 1;
    }

    SDL_Quit();
    return 0;
}