Upvote for me too!!!
Affinity Team, please integrate webp as it is now widely accepted for all browsers. Also Google will give negative pagespeed results when webp is not used. So it would be a BIG plus for webdesigners. I think Affinity is ahead of Adobe application wise, but returning to Photoshop to convert my image feels kind of strange. Using a external converter IMHO is not the way to go!
Have you updated to the latest version of Designer (1.7.1.404)?
Have you run the Designer, opened a file, and exited at least once?
Try deleting the .appinfo files from C:\ProgramData\Affinity\Common\1.0\appinfo\Release