A downloaded webp image from a website could not be opened
It's a WEBP image (developed by Google) and Preview doesn't natively support this file type.  If you right click and select "View Image Info" you can get the image details (this one was done in Firefox)



There are a few ways you can view this image...


WebP Viewer (free).  Available on the App Store.  It's a Quick Look plugin and supports printing.  Supports Safari
Browser Add-Ons:


Firefox: WebP Image Converter
Chrome:  Built In tool

Copy the image and paste it to another application then save it.  I used OneNote and was able to save the image as a JPG.  You can use other apps like Word, Pages, Notes, etc. and achieve the same results.