Using two network adapters, establish separate network connections to the same router. Each will have a different local IP address (e.g., 192.168.1.100 and 192.168.1.101). Because of the way Windows works, you can only use *one* of those network connections for OUTBOUND Internet access anyway (specifically, the one w/ the higher priority under Network Connections). Let’s assume that’s the network connection w/ IP address 192.168.1.100. For any unsolicited INBOUND requests (file sharing, remote desktop, etc.), you could limit your port forwarding to the other network connection and its IP address, 192.168.1.101.
Now frankly, I don’t see much benefit here. I don’t even know for sure if this is what you’re after. There’s enough ambiguity in your question that it’s possible you have something completely different in mind. I just made a guess and provided one possibility. If I’m way off base, then try to describe what you want in more specific terms.