If you try to active evaluation edition Windows server 2016, I must a error message: This Edition cannot be upgraded.
There is only one way to fix this issue: PowerShell

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Open PowerShell in Administrator mode
Run this command: Dsim /Online /get-Targeteditions
Result:
Deployment Image Servicing and Management tool
Version: 10.0.14393.0
Image Version: 10.0.14393.0
Editions that can be upgraded to:
Target Edition : ServerStandard
Target Edition : ServerDatacenter
The operation completed successfully.
As you can see, there are two versions available.
Now run this command to apply the edition and your key that you bought from us or another Microsoft Partner.
Dism /online /Set-Edition: ServerStandard /AcceptEula /ProductKey:12345-ASDFGH-12345-ASDFGH-12345
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Wait couple of minutes and you are asked to restart the server.
Stay tuned