Hi @Mandar Alawani there a no way to create a default policy that gets automatically applies to any new database creation. The Product team are planning to implement that in the future.
You could create a logic app that runs on a schedule, checks for a new database and then updates the PITR/LTR? Tutorial: Create schedule-based automation workflows using Azure Logic Apps
Could you please raise this feedback in the Azure feedback for Managed Instance.
Regards,
Oury