Elements Page Hero serve WebP

Hi,

By default, WordPress doesn't allow WebP files on to be uploaded on its media library. But you can still definitely do it by adding this PHP snippet.

//** *Enable upload for webp image files.*/
function webp_upload_mimes($existing_mimes) {
    $existing_mimes['webp'] = 'image/webp';
    return $existing_mimes;
}
add_filter('mime_types', 'webp_upload_mimes');

//** * Enable preview / thumbnail for webp image files.*/
function webp_is_displayable($result, $path) {
    if ($result === false) {
        $displayable_image_types = array( IMAGETYPE_WEBP );
        $info = @getimagesize( $path );

        if (empty($info)) {
            $result = false;
        } elseif (!in_array($info[2], $displayable_image_types)) {
            $result = false;
        } else {
            $result = true;
        }
    }

    return $result;
}
add_filter('file_is_displayable_image', 'webp_is_displayable', 10, 2);

Reference: https://mariushosting.com/how-to-upload-webp-files-on-wordpress/

Alternatively, you can convert already uploaded jpg files to webp by using a third party plugin.
Read more here - https://kinsta.com/blog/webp/

Will this serve a webp with a jpg fallback?

Will this serve a webp with a jpg fallback?

I'm afraid the snippet is only for allowing you to directly upload your WebP files to the WordPress media library.

Custom image fallbacks to its jpg version will require third party plugins like the one you mentioned. (Imagify)

As to what's the best among the plugins, I'm afraid I can't pinpoint them for you as they're outside GeneratePress support's scope.