Did you perform a Debian version update from Buster to Bullseye?
In fact the time sync package is missing on your system. Therefore the service is failing. Following should bring it back
apt -y install systemd-timesyncd
Did you perform a Debian version update from Buster to Bullseye?
In fact the time sync package is missing on your system. Therefore the service is failing. Following should bring it back
apt -y install systemd-timesyncd