In my opinion enumeration is not an attack technique that blue teamers should focus their defense efforts on. The best way to prevent unauthorized users from accessing this information is by having strict conditional access policies which govern how and from where users are allowed to use their Azure AD credentials. That being said, there is a setting in the deprecated MSOnline PowerShell module which prevents enumeration using the Azure AD graph, which is documented here. I haven’t personally looked into bypassing this or if other functionality in Azure breaks if you enable this