Since Windows Server 2016 until now, with Windows Server 2022: if you want to change Time Server, you will see that the area is grayed out …
The solution is to inject the new Time server (with command line):
Open the command line (depends on the operating system used) Click Start > Windows System > Command Prompt (right click and open with More > Run as administrator).
Copy and paste this command and if necessary modify it
w32tm /config /manualpeerlist:be.pool.ntp.org /syncfromflags:manual /reliable:yes /update
In this command, we’ll change the NTP to be.pool.ntp.org