Elevate access to manage all Azure subscriptions and management groups

 https://docs.microsoft.com/en-us/azure/role-based-access-control/elevate-access-global-admin

Azure AD and Azure resources are secured independently from one another. That is, Azure AD role assignments do not grant access to Azure resources, and Azure role assignments do not grant access to Azure AD. However, if you are a Global Administrator in Azure AD, you can assign yourself access to all Azure subscriptions and management groups in your directory. Use this capability if you don't have access to Azure subscription resources,