OP dances around the key context that this isn’t hidpi, but rather a 3rd party hack that uses hidpi rendering to supersample their “native” 4k resolution by 2x, since the end result looks more pleasing to them than the native 4k render.
When you set it to "more space" it becomes noticeably slower, but not blurry.
Apple basically settles into 220 dpi physical displays (250 moc MacBook Pro), rendering UI at a 2x scale as a default, except for MacBook Airs.