As a full-time administrator, I still find it funny that IPv6 is considered an “insider tip”. (And clearly superior to IPv4.) In fact, there's also a pretty neat trick here:
In fact, your PC has at least 3 IPv6 addresses.
1. An EUI-64: This is generated based on your network card’s MAC address and only changes if your provider assigns you a new network. <- This is good for server hosting.
2. A temporary IPv6 address: This is generated randomly and serves to protect your anonymity on the Internet. (You don’t want to give everyone your MAC address—otherwise, you’d be trackable.) <- You use this to browse the web.
Unfortunately, websites won't help you get a static IPv6 address, since by default it's never used for outbound connections. (Privacy)
To find the static IP address, open the Command Prompt in Windows (cmd) and type ipconfig. There you'll find several IPv6 addresses. The correct one is the one that doesn't say ‘temporary’ or “local.”
Fun fact: IPv6 is 27 years old. Every modern program should fully support IPv6, unless it's using some weird, ancient libraries. But in my opinion, VintageStory has pretty solid programming. (Not like Minecraft Forge, which simply turned off IPv6 in Java. -.-)