Forgot to say - when I enable worksheet protection and share with the email address of the azure app account (which, agian, is the same account at the Microsoft (Office) 365 account, the result of submitting the share dialog is a message about how anyone with the link can access the excel worksheet.
I suspect maybe with protection enabled and "add rows" allowed, the sharing URL for the Excel worksheet might be required. Graph, however, uses a Graph URL. Maybe that is the issue. Sharing would need to be permitted for the account having the e-mail address I shared with, but I think maybe sharing is just allowed via a sharing URL rather than based on the user I've shared with, considering the message that anyone with the URL can access the worksheet despite my (attempt at) sharing the worksheet with a particular account such that the share is permitted via user account rather than being permitted via a particular URL (which is not a Graph URL)