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You can do something like:
git clone -b devel --depth 1 --single-branch https://github.com/pfsense/FreeBSD-ports.git
git clone https://github.com/nhdIT/pfsense-netbird.git
cp -R pfsense-netbird/net/* FreeBSD-ports/net/
cd FreeBSD-ports/net/netbird
make makesum
make package
cd FreeBSD-ports/net/pfSense-pkg-netbird/
make
make package
pkg add -f netbird-0.28.3-whatever.pkg
sysrc netbird_enable=YES
service netbird start
netbird up -m https://netbirdhost -k netbirdkey -interface-name tun12
create new interface, assign to tun12
find netbird ip with netbird status
set static IP to your netbird ip /16
create a gateway, also use your netbird ip
create firewall rules allow all ipv4 protocols on new interface
add service netbird start as an shellcmd
add netbird up as a shellcmd
to install pfsense netbird UI install package https://repo.nhdit.com/netbird-pfsense//pfSense-pkg-netbird-0.0.2_30-amdv2.pkg or the arm one, either way. Then netbird will show under vpn menu. This is not complete, but works for basic needs.