Although I have never been a fan of MicroSoft's designs, many of their wallpapers are very nice. I found this link on Ars to a collection of Wallpaper MS just put up for download and I downloaded a couple to add to my collection. I am not sure why I collect wallpapers. I have hundreds of them, but I have been using the same wallpaper for decades. Sometimes I try a different one, but after a couple day I generally retreat back to the old standby.
Find them here: <https://wallpapers.microsoft.design>