Change Responsive Images Maximum Width of 1600px

You can simply remove that limit, go to your functions.php and add this code.

function remove_max_srcset_image_width( $max_width ) {
    return false;
}
add_filter( 'max_srcset_image_width', 'remove_max_srcset_image_width' );

If you want to increase, go to your functions.php and add this code.

function custom_max_srcset_image_width( $max_width, $size_array ) {
    $max_width = 1800;
    return $max_width;
}
add_filter( 'max_srcset_image_width', 'custom_max_srcset_image_width');