@m1ster
Hello!
You can't build Hummingbird or the AirPVN Suite in FreeBSD because OpenVPN3 AirVPN library needs various modification for FreeBSD, you will not be able to even compile it at the moment.
We have plans to port the AirVPN Suite to FreeBSD later this year, but first we need to adapt the library, which might be or not a trivial task, and we must release a new Eddie Android edition version before the summer is over.
At the moment you only have the Linux binary compatibility mode option (try with Hummingbird, as Eddie will have too many complications due to Mono), and of course OpenVPN 2.5.2.
Hummingbird and the Suite support and have always supported pf, the default FreeBSD firewall, but different directory tree and some other issue may cause trouble. https://docs.freebsd.org/en/books/handbook/linuxemu/
Anyway we assure you that FreeBSD support improvement with native applications remains our goal for 2021. Our FreeBSD users are many (25% of our Windows customers, and 20% of our Linux customers, who are currently the absolute majority), not to mention the system outstanding superiority, so stay tuned.
Kind regards