I think your understanding is right.
We need at least SCCM 2006 in order to support it as a Windows 10 client.
Besides, according to your client scenario, use Windows 10 Servicing or Task Sequence Upgrade should be more suitable, look at this similar case, the user here choose Windows 10 Servicing for upgrade.
https://learn.microsoft.com/en-us/answers/questions/391799/best-method-of-windows-10-20h2-deployment.html
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