You start by adding ipv6 and serving both. One side needs to move first. Content providers or isps.
The big tech companies are using ipv6. In the UK the isps are mostly offering it too.
Host both and help us move towards dropping Ipv4 some day. It's not going to happen in a day.
This is my biggest bugbear about a lot of UK isps. They are dynamically allocating ipv6 prefixes for absolutely no good reason.
I've only ever done ipv6 using Linux directly as a firewall or a mikrotik router. So cannot help with pfsense I'm afraid.