On a Windows Server 2016 Datacenter Edition (with GUI) open the cmd line and type:

dism /online /add-package /packagepath:"C:\Windows\servicing\Packages\Adobe-Flash-For-Windows-Package~31bf3856ad364e35~amd64~~10.0.14393.0.mum"

(BTW. Adobe Package is already on disk. You just activate it)

+ Reboot

https://blogs.technet.microsoft.com/bernhard_frank/2016/11/24/add-flash-player-to-server-2016/