Hi @oQcS3JJ2xdjHwF67 ,
Welcome to Microsoft Q&A!
How do you upgrade/change W10 Ent LTSC 1809 to W10 Ent Semi-Annual Channel (SAC)?
Please see this official document: https://learn.microsoft.com/en-us/windows/deployment/upgrade/windows-10-upgrade-paths
As for 21H1, It does not update itself indicating that your environment is not currently eligible for 21H1.
See this: https://support.microsoft.com/en-us/topic/kb5000736-featured-update-to-windows-10-version-21h1-by-using-an-enablement-package-75a01e67-3b5f-4677-8efe-42852e41c7cf
Best regards,
Seeya
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