Looking for a way to block user accounts from entering admin portal.

I’m currently working on a project where I need to restrict user access to the admin portal. The issue I'm running into is that both admin and user accounts are currently able to access the portal, which is a problem. 🚫

What I want:
I want to make sure that only the admin can access the admin portal, and users should be restricted from entering.

Any guidance or tips would be greatly appreciated! 🙏

Thanks in advance! 😊