Google posted that vignette ads are now supported on wider screens. Google wrote “vignette ads now support a larger range of screen sizes. For sites that have vignettes turned on, vignette ads will soon start to appear on wider screens such as desktop.”
Google said experiments displaying vignette ads on wider screens have performed very well, which is why it has fully launched it for wider screens.
Google said that if you want to not to show vignettes on desktop, you can turn this option off using the new “Wide screen” control in your Auto ads settings. Note that wide screen vignettes won’t start serving until after November 3, 2020.
You can learn more about this over here.
Forum discussion at Twitter.