It's not interface dependent with access-groups like on, say, an ASA.
You get a separate firewall for cellular failover, for data usage control.
Then you have a general L3 firewall. As per the screenshot below, inbound traffic will be restricted according to the other rules on the Firewall page:
If you've got 1:1 NAT or 1:Many, you can restrict allowed remote IPs directly on those statements if you really need. (I'm personally skeptical on the value of IP blocks, since spoofing is a thing.)