This script will categorize items into their own section:
-In-Stock
-Pre-Order
-Back Order
-Out of Stock

And users get option to show or hide each sections, except for the in-stock section, which is always shown.

Unfortunately, this is not a "true" filter since it only works as a filter for each r###lt page.

For best r###lt, I strongly suggest to also install this script as well https://greasyfork.org/en/scripts/22077-amiami-200-items.