That statement is incorrect. Microsoft Entra tenants are NOT created IN an Azure subscription.
Microsoft Entra tenants and Azure subscriptions are two distinct entities. You don't create one INSIDE the other.
You can create any number of Microsoft Entra tenant independently of any Azure subscription. However, to create an Azure subscription, you have to have at least Microsoft Entra tenant. That tenant contains identities that you can use to access the Azure subscription (by associating that subscription with the tenant).
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hth
Marcin