WebP images

I'm not sure if this is a GP issue, but if not I'd appreciate some advice on where to look for help.
I am building 2 new sites with the latest GP Premium, WP 5.9 and PHP 8.0.
When I go to upload a WebP image, I get an error message saying I must convert them to JPG or PNG.
I have built my own site using PHP 8.0 and I don't get the error message. And the active PHP extensions are the same for all.
The only things that are different are the version of WP and GP. Yet, my own site has since been updated to both the latest GP and WP and can still load WebP images.
I haven't seen the issue raised in either GP or WP forums, which has left me really scratching my head.