If you are searching for how to enable flash player on Windows Server 2016 you should keep in mind that you must install RDSH as MS recomendation.
But if you havent license for RDHS and flash player that all you need then just run from cmd:
dism /online /add-package /packagepath:”C:\Windows\servicing\Packages\Adobe-Flash-For-Windows-Package~31bf3856ad364e35~amd64~~10.0.14393.0.mum
And of course, you must restart server. Thanks to God that no reboot requred for at least ip address change like in windows 98.