If you have already downloaded the .webp file and can't open it:

Right-click and select or "Open image in new tab" .

Paste it into an image editor (like Paint, IrfanView, or Photoshop) and save it as a file.

Almost all modern browsers (Chrome, Firefox, Edge, Safari) can open WebP files natively.

Use Adobe Express for a quick online conversion to JPG.

How To Install WebP Plugin for Photoshop CS5 - Adobe Community

If the site restricts right-clicks, you can use the Vivaldi Forum method:

If using an older version of Photoshop, you may need the WebPFormat plugin to open or save these files.