Does System Mechanic Ultimate Defense have a firewall?

No, System Mechanic Ultimate Defense does not provide a firewall option. However, it has a built-in Network Scanner which scans for open ports. If it finds any suspicious open port, it lists it in the results. Then, you can use Windows’ Firewall & Network Protection to close the ports in question. If it happens that you have other firewall software installed, then you have to use that software to manage firewall options and ports on your computer.