/*This allows to upload webp files */
function webp_file_ext( $types, $file, $filename, $mimes ) {
    if ( false !== strpos( $filename, '.webp' ) ) {
        $types['ext'] = 'webp';
        $types['type'] = 'image/webp';
    }
    return $types;
}
add_filter( 'wp_check_filetype_and_ext', 'webp_file_ext', 10, 4 );

function webp_file_upload( $mimes ) {
    $mimes['webp'] = 'image/webp';
  return $mimes;
}
add_filter( 'upload_mimes', 'webp_file_upload' );

/*Preview Webp files */
function preview_webp_thumnail($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', 'preview_webp_thumnail', 10, 2);