What are the differences in visual quality between a video that has been downscaled from 4K to 1080p and a video that is originally in 1080p resolution?

A video that has been downscaled from 4K to 1080p may have better visual quality than a video that is originally in 1080p resolution. This is because the downscaled video retains more detail and clarity due to the higher resolution it started with. However, the difference in visual quality may not be very noticeable to the average viewer, especially on smaller screens.