You should NEVER set a computer to be in the DMZ. that leaves it completely accessible to the world of hackers.
Only ever forward single ports or small ranges of ports as necessary.
Friends outside your house always need your "public" ip address nothing more. (https://ip4.me or https://ip6.me)
Your "ipconfig" (windows) "ip addr" (linux) ip address is only needed if your are inside the same house on the same network.
And it's also only used to setup the port forwarding correctly
P.S. UPNP should also be turned off, or other random programs could easily open ports on your router without your knowledge.
Sidenote: according to the image you provided, you would set the following...
Add Rules Manually
Custom service name: Vintage Story
Service: Other
protocol: TCP
External host: BLANK
Internal host: ip address for the machine hosting the server
External Port: 42420
Internal Port: 42420
Be Safe,
I_Died_Tryin