Recent versions of Windows 10 (2004-21H1) share a common core operating system with the same files so can be easily upgraded to 21H2 using an enablement package (windows update KB5003791). This small update (164KB) allows an easy and quick feature update.

More info from Microsoft: https://support.microsoft.com/en-us/topic/kb5003791-update-to-windows-10-version-21h2-by-using-an-enablement-package-8bc077be-18d7-4aac-81ce-6f6dad2cd384

Microsoft state that it cannot be install manually but you can download the MSU files below:

• x64 - http://b1.download.windowsupdate.com/d/upgr/2021/11/windows10.0-kb5003791-x64_14e7547b08f1b29cae6e41c9f7
• x86 - http://b1.download.windowsupdate.com/d/upgr/2021/11/windows10.0-kb5003791-x86_ac1fc53b104c6ce0ffa50b70af754b81e56829ce.msuda5f1347d9955c.msu
• arm64: http://b1.download.windowsupdate.com/d/upgr/2021/11/windows10.0-kb5003791-arm64_047071577e1aa33883b851a8b2c749b1e723e369.msu

Then it can be silently installed with the command:

WUSA.EXE windows10.0-kb5003791-x64_14e7547b08f1b29cae6e41c9f7da5f1347d9955c.msu /quiet /norestart /log:c:\temp\21H2-Update.log

After install the machine needs to be rebooted and is then on the latest version of Windows 10.