Websites increasingly serve images as WEBP because it saves bandwidth. But when you save those images, some older apps - image editors, office suites, printers' software - refuse to open them.
Steps
Open WEBP to JPG (or WEBP to PNG if the image has transparency)
Upload the .webp file
Convert and download the universally-compatible file
Choosing the output
JPG - smallest result, ideal for photos; transparency is flattened to white
PNG - keeps transparency and pixel-perfect detail; larger files
If the image is a logo or icon with a clear background, always pick PNG
Going the other way
Publishing on the web yourself? Convert JPG or PNG to WEBP for noticeably smaller files - every modern browser supports it.