With Magento's recent 2.4 update, a new feature known as "Multi-Source Inventory" has been enabled. Modern Retail does not support Magento's Multi-Source Inventory, and clients should not enable it. This article will include more details.
Currently Modern Retail does not support Magento's Multi-Source Inventory feature. Modern Retail expects to be able to support Multi-Source Inventory down the road; developing support for this feature is on our development roadmap for this upcoming Summer. If you would like to use Multi-Source inventory, or are otherwise curious about the information laid out in this article, please feel free to let us know with a support request.