Getting Started with Group Managed Service Accounts
Preparing the domain
Perform these steps to prepare the domain:
Step 1: Run ADPrep /domainPrep
You will then see:

Note: Active Directory Domain Service requirements
The Active Directory schema in the gMSA domain's forest needs to be updated to Windows Server 2012 to create a gMSA.
*-> You can update the schema by installing a domain controller that runs Windows Server 2012 or by running the version of adprep.exe from a computer running Windows Server 2012 . The object-version attribute value for the object CN=Schema,CN=Configuration,DC=Contoso,DC=Com must be 52.
Reference:
https://learn.microsoft.com/en-us/windows-server/security/group-managed-service- accounts/getting-started-with-group-managed-service-accounts
https://www.koolaid.info/dude-wheres-my-managed-service-accounts/