I see that I have the Out-of-Stock threshold in my admin panel, how could I use it in order to have more items in my products in stock then I really have?
And how does it works?
You can use a negative amount in order to have more salable items than you really have in stock.
Use a negative value for this threshold to set the maximum amount of products that can be backordered before the product is truly considered out of stock. This amount adds to the salable quantity. The value set at the product level overrides any value set at the global level.
The formula for the Salable Quantity is (Quantity - (Out-of-Stock Threshold)).
The following is an example:
Quantity: 25 Notify for Quantity Below: 10 Only X left Threshold: 5 Out of Stock Threshold: -50
The Salable Quantity for this product is 75 (25 - (-50)).
When customers purchase more than 25 products, new orders enter as backorders. As the product’s Salable Quantity reduces to 5 (70 items have been sold), the Product page will display a message Only 5 left on the storefront. When the Salable Quantity reaches 0, the product is displayed as Out of Stock in the storefront.
Reference: Magento 2 DevDocs - Out-of-Stock threshold
This does not work on M2.4.2 CE.
Every time you save the product and then go back into it, it has reverted back to 0, it does not save the '-' figure.
The problem with an OOS value of Zero is that with backorders enabled (at product level), zero is calculated as infintely back orderable and therefor allows potential massive overselling.
Check your reservation table to your item in the database and check if your CRON, to make sure you have it running well to do the calculations.
If you don't need to have a threshold in all your products, you can disable it and in the products that you don't need to manage stock, you can disable the "Stock management" directly via the product page in the admin panel.