When you buy Microsoft 365, you don’t receive an Office product key. Instead, you purchase a one-year license that is stored in your Microsoft account. Since these versions don’t have a traditional product key, key finder tools are not able to recover the product key for the versions of Office used in Microsoft 365. However, you can install the new versions of Office locally without a subscription by purchasing a one-time product key. In this case, the product keys are then stored in the registry as usual.
The Magical Jelly Bean Keyfinder only recovers product keys up to Office version 2010. Other similar tools are able to find the serial number for newer versions of Office, as long as these versions are used locally and not as part of a Microsoft 365 subscription.