Hi @Prateek Rana ,
Description of "Name" parameter of Get-AzPolicySetDefinition cmdlet says "The policy set definition name" which is not correct because "Name" parameter takes ID of the policy set definition id but not the name of the policy set definition as shown in below screenshots. So, I have raised this issue with Az PowerShell engineering team to either change the parameter name from "Name" to be more appropriate and/or update the description of the Name parameter to avoid confusion.
Meanwhile, to get policy definition details related to a policy set definition, use below command. For illustration of sample output, check below screenshots.
(Get-AzPolicySetDefinition |?{$_.Properties.DisplayName -eq "NIST SP 800-171 Rev. 2"}).Properties.PolicyDefinitions
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