Hello,
I understand you want to upgrade your Windows Server, but please note that Windows Server versioning is different from Windows Client versioning.
The 20H2 versioning refers to Windows client systems (Windows 10). On the Server side, Microsoft follows a Long Term Servicing Channel (LTSC) scheme for their Windows Server releases. These include versions like Windows Server 2019 or the most recent, Windows Server 2022.
So, if you want to upgrade your Windows Server 2019 (which is equivalent to version 1809 in client terms), you would be upgrading to Windows Server 2022 (the most current version as of now).
Just like the similar issue below:
Update Windows Server 2019 to 20H2 - Windows - Spiceworks Community
Best Regards,
Hania
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