There is nothing good about it; regions cannot be smoothed out. This is inevitable, anti-aliasing only works when you know the background colors so that you can blend correctly. This is not an option for windows; the design background is unpredictable. If this is a splash, you can fake it by taking a screenshot and drawing a fake window on top of it. Not working for more than a few seconds.
It is best to keep the angle within a small radius so that it is not noticeable. Also use the ZoomIt tool from SysInternals and carefully look at the rounded corners of the program, for example, Windows Media Player. Pay attention to the gray tones that he uses to draw the border.
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