Hi @Hudson Spangler ,
Per my test, I could reproduce the same issues on my end. Looks like it's not supported using sharingUrl to get the workbook.
Currently, we have to get the workbook like this:
https://graph.microsoft.com/v1.0/drives/<driveID>/items/<itemID>/workbook
You can get the driveID and ItemID in the response when accessing its driveItem.
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.