Couple things to add:
Form is still active even if account is in Azure AD recycle bin.
It is possible to find ObjectID of form owner by using method found in this thread :
1. Access the form using this designer direct URL https://forms.office.com/Pages/DesignPage.aspx?origin=shell#FormId=%3CHere
2. Inspect the network traces. You will find a request similar to this
https://forms.office.com/formapi/api/72f988bf-86f1-41af-91ab-2d7cd011db47/users/e5351c57-d147-418e-89ab-3a3d50c235b6/light/forms('v4j5cvGGr0GRqy180BHbR1ccNeVH0Y5Bias6PVDCNbZUOUg4TkZJUEswSVQ1ODhNNkpHVVlMMldPTi4u')?$select=id,...
3. The ID in bold is the AAD ID of the user
4. Use https://developer.microsoft.com/en-us/graph/graph-explorer to run this request to retrieve the username and email address of the owner https://graph.microsoft.com/v1.0/users/<UserID>