If the server is running an evaluation version of windows server 2016 standard or windows server 2016 datacenter you can convert it to a retail version as follows.
Windows server 2016 standard evaluation this edition cannot be upgraded.
If you have installed windows server 2019 windows server 2016 standardevaluation or datacenterevaluation edition to try the new features of the microsoft server platform you can download windows server 2019 free trial or windows server 2016 evaluation here after registering you have 180 days to test it.
But on one server it went on going for 16 hours and i had to eventually wipe it out and install fresh with server standard disc on windows server 2012 though it used to be smooth.
I tried that recently with windows server 2016 standard evaluation and it returned the message this edition cannot be upgraded.
During this period all features of windows server 2019 2016 are available to you.
Fortunately upgrading is as simple as using the command line.
In this case install an additional domain controller on a server that runs a retail version and.
If the server is a domain controller you cannot convert it to a retail version.