Support for WebP images / photos
As far as I can tell, Evolution 3.34.x doesn't render WebP images in the mail view (whether as part of an HTML email, or as an un-foldable attachment), yet in theory it should be able to, since it's based on WebKit.
Web mails and mobile mail clients already support WebP. In GNOME, gThumb and GIMP also support it.
Some samples are available on https://developers.google.com/speed/webp/gallery1