@kenlouise I’m currently going through the oauth verification process.
My app needs only needs verification for the sensitive scopes, but even this is taking months. Going back and forth.
Calendar API may be a restricted scope which might need an external agency verification prior to Oauth approval( might cost you around 15k to 75k . Not sure.)
I can understand how tedious it could be.
Though I do not have any tips to share, I wish you good luck to get the approval soon.