Does your friend setting up port forwarding on their pfSense not help in your scenario?
This hs a good diagram to understand the options
https://rajsinghtech.github.io/claude-diagrams/diagrams/netw...
You can scope it to just your IPsec service, or whatever it is your hosting, or you can enable full cone for the whole subnet.
It is not DNAT, nor is it port forwarding. If you host a SIP proxy, SBC or peer to peer gaming, it will enable these use cases as well.
https://docs.netgate.com/pfsense/en/latest/nat/outbound.html