SDL_SetWindowBordered - Man Page

#include <SDL3/SDL_video.h>

bool SDL_SetWindowBordered(SDL_Window *window, bool bordered);

This will add or remove the window's SDL_WINDOW_BORDERLESS flag and add or remove the border from the actual window. This is a no-op if the window's border already matches the requested state.

You can't change the border state of a fullscreen window.

window

the window of which to change the border state.

bordered

false to remove border, true to add border.

for more information.

This function should only be called on the main thread.

This function is available since SDL 3.2.0.

SDL_GetWindowFlags(3)