http://ciisqbg45nggykdl6rjdrq3wc64csga4vkphu66qsi65mypeitqedoad.onion/pfsense
So if you don't have one, click on Interfaces -> LAN and change "IPv6 Configuration Type" to "Static IPv6", then scroll down to "Static IPv6 Configuration" and choose a subnet (I.e., fd00:20:20::/64). Next, click the Interfaces menu at the top, then Assignments. On this page, next to tun_wg0, click the green Add button, then the blue Save button. Click the Interfaces menu at the top again, and there should now be an OPT1 entry, so click on that.