This is an updated version of this guide. I hope it gets moved soon to the guides section.
This guide should be complete now, but please note that the IPv6 port forwarding might not be 100% complete. Any advice is appreciated.
Disclaimer
In general, DO NOT TRUST ME! I'm not a security expert. I do not know what I'm doing here!
This guide is based on:
OPNsense 24.7.12_4-amd64
FreeBSD 14.1-RELEASE-p6