Hello,
I'm sorry, but it is not possible to activate a Windows Server 2016 license on a Windows Server 2019 installation. Each version of Windows Server requires its own license key.
To activate your Windows Server 2019 installation, you will need to obtain a valid license key for that version of Windows Server. You can purchase a license key from Microsoft Store or from an authorize reseller. Once you have a valid license key, you can activate your Windows Server 2019.
About how to activate Windows, please refer to this link:
Best Regards,
Hania Lian
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