Is it mandatory to enable “Allow negative inventory” when creating a product with no inventory?

Yes, you need to enable the “Allow negative inventory” option when you create a product that does not yet have any inventory recorded and you are not going to enter quantities at that time.

If this option is not enabled, the product will not be displayed on the page, since the system interprets it as an unavailable product.

This option allows you to publish the product even though it does not yet have any quantities recorded in inventory.