We recently needed to open a .webp file to resize it to match the other logos needed on a website. We discovered someone has created a plugin to work with Photoshop. We are using an older copy of Photoshop CS6. Here is link to the Plugin:

https://github.com/webmproject/WebPShop/blob/master/bin/WebPShop_0_2_0_Win_x64/WebPShop.8bi

We downloaded it and put it into “C:\\program files\adobe\photoshop(64 bit)\plugins\“. We did need admin rights to paste the file. Restarted Photoshop and we could open the files

Let us know if this helped you….