Thank you for posting this in Microsoft Q&A.
I understand that there is no service administrator mentioned in our documents. The article https://video2.skills-academy.com/en-us/azure/role-based-access-control/classic-administrators only talks about co-administrators. However, the same applies to service administrators as well.
In RBAC there is only have one owner role and one contributor role on subscription level. These roles are highest privileged role in RBAC on the subscription level. Other built-in roles are used to handle other resources like, VM's, storage etc.
Owner role is the one which is equivalent to service administrator and co-administrator role in classic subscription administrator role.
The rest of the built-in roles allow management of specific Azure resources. For example, the Virtual Machine Contributor role allows the user to create and manage virtual machines. For a list of all the built-in roles, see Azure built-in roles.
You refer below article,
For service administrator, you can have the same user account have owner role assigned on the subscription.
To replace service administrators with new role, you can follow below article,
Note: In the above article it is mentioned as co-administrators, but you can consider the same steps for service administrators as well.
Let me know if you have any further questions
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