I would like to get some clarification about OneDrive and Drives of a user.
There are many examples in Microsoft Graph where a request to get user's drive occurred with help of "drives":
/users/{userEmail}/drives/{drive-id}/items/{item-id}/children
In documentation it states that "Most users will only have a single Drive resource".
What are there cases where a user could have multiple drives?
I found a related question where it said this is not possible now but the last answer is from 2015 and it links to older release notes: Create multiple OneDrive drives.
For a user resource, there is only a single drive. It is possible that at some point this would change but I'm aware of any mechanism for generating additional drives today.
The reason for the /drives/{drive-id} pattern however is because this API covers more resources than just a user. For other resource types, multiple drives is quite common. A SharePoint site for example may have any number of "Document Libraries", each of which would surface within the OneDrive API as a distinct drive.