Please check this, As of August 31, 2024, Azure classic administrator roles (along with Azure classic resources and Azure Service Manager) are retired and no longer supported. If you still have active Co-Administrator or Service Administrator role assignments, convert these role assignments to Azure RBAC immediately.

You need to assign the roles https://learn.microsoft.com/en-us/azure/role-based-access-control/classic-administrators?tabs=azure-portal#prepare-for-co-administrators-retirement