Currently, we install InventoryCatalog module with Default Stock and Source and their linkage.

But along with that we need to create Stock_Item index.

That will make an experience of Single Stock merchant seamless as well as simplify Testing of Reservations and Stock calculation services which are dependent on Stock Item index

Read this document for more details - https://github.com/magento-engcom/msi/wiki/The-Concept-of-Default-Source-and-Domain-Driven-Design