Does OAuth verification / CASA apply to gmail.readonly via domain-wide delegation only?

We’re building a B2B SaaS. A service account reads Gmail with gmail.readonly only, through domain-wide delegation that each customer’s Google Workspace super admin authorises in their Admin console. There’s no OAuth consent screen or user sign-in flow, and no Marketplace listing. Does this need OAuth app verification and a CASA assessment? If so, how do we submit it without a consent flow?