Microsoft released a set of official Wallpapers. The set includes 19 wallpapers and each of them is available in different sizes.
The new Wallpapers are available on the Microsoft Design page. Scroll down until you find the image you like.
The site provides additional details for each image. On the left, you'll see the purpose of her curation image, while on the right, there is some information about its editors.
To download a single image, click the download button at the bottom right. One will come down archive ZIP, which will contain the image you selected. 
The sizes are different as the images are aimed at many different devices Android, Desktop, Surface Duo and iPhone. Choose the image size that fits the analysis of your desktop.
Microsoft Design has 19 wallpapers that include:
- Icon System Celebration
- Microsoft 365 Vision
- Office Icons
- Pride
- Surface Duo
- Surface go 2
- 3 Laptop Surface
- Surface Pro X
- 3 Surface Book
- Surface Pro 7
It is also possible to download the entire set. At the bottom of the page, click Download All. You will download a 170MB ZIP file with all the images and all their sizes.
https://wallpapers.microsoft.design/
