When using the Fusion API, you can do operations with it on behalf of the user that is logged-in inside the product.
Previously, that was not possible with the Manufacturing Data Model API, and you needed to provide a login UI to get an access token that you could use to call that API.
Just like we've had a fusion360:// protocol for quite a while that lets you open files in Fusion, now we also have the mfgdm:// protocol you can use to send requests to the Manufacturing Data Model API on behalf of the logged-in user.
You can find samples here: Gets all properties using GraphQL
Also check out Using the MFGDM API with the Fusion desktop API