What is NOT supported with Azure Site Recovery

Besides disaster recovery of on-premises and Azure VMs,Site Recovery can help with the following types of migration:
Migrate from on-premises to Azure: Migrate on-premises Hyper-V VMs, VMware VMs, and physical servers to Azure. After the migration, workloads running on the on-premises machines will be running on Azure VMs.
Migrate within Azure: Migrate Azure VMs between Azure regions.
Migrate AWS: Migrate AWS Windows instances to Azure IaaS VMs.

It has some limitations though -

ASR does not support the recovery of machines with desktop OS’es.  (Also, some client virtual desktop flavours (eg. Windows 7) are not yet supported for licensing in Azure.)

Failback to on-premises from Azure VM with managed disks is not currently supported.

Replicating and recovering Azure virtual machines from one region to another region with ASR using PowerShell, CLI & REST API is not currently supported

You can only replicate a classic virtual machine and recover it as a classic virtual machine. You cannot recover it as a Resource Manager virtual machine using ASR.

Replication of VMs with Standard or Premium Managed disk between Azure regions using ASR is not supported 

Azure Backup and ASR can't protect the same workload

No support for UEFI conversions

Also see:
What is NOT supported on Azure Virtual Machines
What is NOT supported with Azure Site Recovery

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