The Xbox One X indeed has the ability to upscale 1080p content to 4k resolution, similar to how some Blu-ray players can upscale to near 4k. When the console is set to a 4k UHD resolution, all content on the console, including games and apps, will be displayed in 4k. For content that is not natively 4k, such as games encoded for 1080p, the Xbox One X will upscale it to 4k. However, it's important to note that unlike some Blu-ray players, the Xbox One X does not automatically upscale 1080p movie discs to 4k. For a movie to be displayed in 4k, it must be a 4k movie disc.
It's also worth mentioning that the Xbox One X has received positive reviews as a 4k Blu-ray player. It is capable of playing 4k Blu-ray discs and UHD digital video, making it an ideal option for all of your 4k media needs. The Xbox One X's 4k capabilities are considered to be of higher quality than the Xbox One S, which has upscaled 4k rather than native 4k resolution. Additionally, the Xbox One X also offers impressive upgrades for 1080p content, making it a versatile option for a variety of resolution needs. However, it's worth noting that the Xbox One X does not support Dolby Vision or HDR10 for 4k Blu-rays, so you will have to make do with standard HDR10 high dynamic range.