https://www.drupal.org/project/imagewebp lets you upload a regular jpg/png which converts it into webp, but how to upload already a file that is in webp?
Adding it as one of allowed extensions in the field setting does not work.
update As an alternative this can be solved with https://www.drupal.org/project/file_entity, but this is for the file field and not image field.
The question is about image field. Because in production site that already has image field in use with many images and pages active, it needs .webp extension support added to already existing image field.