Some of my images online and most my images in downloads are now in WebP format (even in the EPUBs). Seeing them requires you to use (PC, Mac, Linux, or Android) Google Chrome, Google Chrome OS, (PC, Mac, or Linux) Firefox, (PC or Mac) Microsoft Egde (since January 2020) or iOS (iPhones and iPads) 14 or Mac OS 11.
Yes WebP now works on Macs with Safari and iOS (if you are on a new enough version). iOS 14 (and 15) will even work as far back as the iPhone 6S. This free software update was released in the fall of 2020 for Macs, iPads, and iPhones.