Hi,
Currently, there is no such option as sleep mode on Azure VMs. You can add your feedbak here
You can try out with start/stop mode.
https://learn.microsoft.com/en-us/azure/automation/automation-solution-vm-management
You can also have a look on this -
https://learn.microsoft.com/en-us/azure/lab-services/classroom-labs/how-to-windows-shutdown