Debian 11: (bullseye): http://debian.beagleboard.org/arm64/

deb [arch=arm64] http://debian.beagleboard.org/arm64/ bullseye main
#deb-src [arch=arm64] http://debian.beagleboard.org/arm64/ bullseye main

keyring:

apt-key adv --keyserver keyserver.ubuntu.com --recv-key D284E608A4C46402