Almost all modern browsers (Chrome, Firefox, Edge, Safari) can open WebP files natively.
Note: If you need the image in a different format (like JPG or PNG), you can use a browser extension like Convert WebP to PNG / JPG to save it directly in your preferred format.
How To Install WebP Plugin for Photoshop CS5 - Adobe Community
If using an older version of Photoshop, you may need the WebPFormat plugin to open or save these files.
If you have already downloaded the .webp file and can't open it:
If the site restricts right-clicks, you can use the Vivaldi Forum method:
Use Adobe Express for a quick online conversion to JPG.