Does Azure automatically replicate existing blobs when we change the storage redundancy type from say LRS to ZRS/GRS? or do we have to manually replicate these objects? I know AWS does not auto replicate so i want to know if same applies to Azure as we need to implement that in one of our existing solutions
It is not automatic, after you change the storage redundancy type, you need to either perform a manual migration or request that Microsoft performs a live migration.
For details see: https://learn.microsoft.com/en-us/azure/storage/common/redundancy-migration?tabs=portal