I have posted that howto (Bullseye: building piaware from source code) at two places:
(1) 11 days ago:
https://discussions.flightaware.com/t/raspberry-os-raspbian-updated-to-debian-11-bullseye/80048/3
(2) Yesterday :
https://discussions.flightaware.com/t/piaware-for-raspberry-pi-zero-2-w/79956/9