Depending on what kind of window you want, you can still get a modal in one line with the Windows SDK

           MessageBox(NULL, "Something Went Wrong", "Error", MB_ICONEXCLAMATION | MB_OK);

A full windows window including a message handling loop is only about 50 lines of code [0]

[0] https://learn.microsoft.com/en-us/windows/win32/learnwin32/c...