@Ryan Veteze
Hi,
If you choose to buy Windows Server 2019.
You cannot downgrade directly. You have to a fresh install with the Server 2016 media.
For Windows Server 2016 Essentials: You can convert to the full retail version by entering a retail, volume license, or OEM key in the command slmgr.vbs.
https://learn.microsoft.com/en-gb/windows-server/get-started/supported-upgrade-paths
At present, the official channel only supports the purchase of Server 2019, you can consult the activation center:
https://www.microsoft.com/en-us/licensing/existing-customer/activation-centers
Hope above information can help you.
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