I loathe windows, but I did just double check because this sounds inept even for M$ -- Win photos will absolutely open .webp, but it's not the default program for whatever reason and it just defaults to edge / your_default_web_browser_here. Which is just impressively on brand for microsoft. Even when they have a feature they hide it to, idk, make themselves look even worse? Why not!

proof

(FWIW this is a clean install, I do not have any non-default codecs installed)