@Raja, Soumya Welcome to Microsoft Q&A, thank you for posting your here!!
We have tried with the latest Az PowerShell Az i.e 10.3.0 and was able to enable the SFTP on Storage account.
Also make sure to check if the version of Az.Storage module is latest ie. 5.10.0
Hope this helps!
Kindly let us know if the above helps or you need further assistance on this issue.
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