Hi,
In regards to your issue, here're my suggestions:
(1)A computer that is a member of a domain is configured by default to synchronize from the domain hierarchy.
(2)If the computer is not a member of a domain, it must be manually configured to synchronize with a specified time source. Manually-specified time sources must be a NTP server.
I want to confirm that
(1) Is your computer in a workgroup or domain environment?
(2) Is the 'a link-local IPv6 source' you mentioned is configured as a NTP server?
Under different situations, there will be different configuretion.
About Windows Time service tools and settings, you can refer to:
https://learn.microsoft.com/en-us/windows-server/networking/windows-time-service/windows-time-service-tools-and-settings
About How to configure an authoritative time server in Windows Server, you can refer to:
https://support.microsoft.com/en-us/help/816042/how-to-configure-an-authoritative-time-server-in-windows-server
About How the Windows Time Service Works, you can refer to:
https://learn.microsoft.com/en-us/windows-server/networking/windows-time-service/how-the-windows-time-service-works
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Regards
Gloria