Hello Tom.
Sorry to hear you're having trouble uploading the images in webp.
I looked into the settings and I had not had webp enabled.
I enabled webp uploads and did a test.
The image in webp is uploading but for some reason the thumbnail is not generating.
I'll look into the issue further tomorrow.
Thanks for posting this question and alerting me.
Hopefully I can get the issue resolved soon for webp images.
However if you still want to upload them in another form such as jpg you can use this easy to use online image converter that I've used before myself.
https://ezgif.com/webp-to-jpg
Just an update as well I'm also still working on the filevek.com file hosting site and it may be an additional month before it goes online.
I want to ensure the bugs are all worked out as much as possible.
Regards
Chad