E: The repository ‘http://flightaware.com/adsb/piaware/fil
es/packages buster Release’ no longer has a Release file.
N: Updating from such a repository can’t be done securely,
and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and u
ser configuration details.
pi@piaware:~ $
This is a problem on our side, the mirrors are meant to be excluded from http → https redirect for exactly this reason but that rule has been lost somewhere. I’ve asked ops to take a look. Sorry for the hassle!