magento2 – How does Magento 2 Inventory works when an order is made?

The deafult behavior is that the stock is reserved when the order is placed (not when the product is added to the cart). Only the first customer will be able to finish checkout process. Right after order placement quantity remains the same BUT saleable quantity decreases (in your case qty = 1 and saleable qty = 0). When you ship the order the qty decreases. When you cancel the order, saleable qty increases back to 1.