I can't add backorder products to the cart
WooCommerce comes with a backorder feature where you can take orders of items even when the stock quantity is zero or lower.
If your backorder products are set to 'In Stock' then they can be ordered - either from the WooCommerce table view or the single product page. If they are set to 'Out of Stock' then the Add to Cart button will be disabled. This is a WooCommerce function and isn't related to WooCommerce Product Table.