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.