Why does my time synchronization always fail

hi,

your configured NTP server 10.4.128.211 isn't responding back, that's why it fails. you can edit your configuration in /etc/systemd/timesyncd.conf, it might also be located in /etc/systemd/timesync.conf.d/ directory.

by the way with PVE 7 we don't use systemd-timesyncd by default anymore, instead we use chrony.