I don't think this is working. I opened tickets #1095517, #1090749, #1090749 with MSI support because the NAT loopback/reflection was working over WiFi but not over a wired connection. My tickets didn't mention NAT loopback or NAT reflection because I didn't know these terms at the time for the issue I was experiencing. Now with firmware 723375 it looks like NAT loopback is broken for WiFi as well. I'd setup a Split DNS but that doesn't work with the public certs I have on most of the port forwarded services. Hopefully MSI takes this feature seriously even for gamer focused routers. All my previous routers (from other manufacturers) supported this without issue.
[UPDATE] Nat loopback/reflection/hairpinning definitely does not work with this router. I setup Split DNS on my LAN which resolved the issue I was having trying to access the services I have exposed via port forwarding from inside my LAN. The cert issue I was worried about turned out to not be an issue since the IP is not in the cert.