Standard and Managed DNS services End of Life was announced in Summer 2019 with an expiry date of May 31, 2020 and all service users were notified. Recently this date has been extended to May 31, 2022. Prior to this date you will need to migrate your services accordingly to avoid disruption. Unfortunately it might require you to purchase a new router or use a software based update client. As you shared currently OCI DNS does not support dynamic DNS.
Oracle + Dyn