Flash player is included in Windows Server 2016 but not actived for IE by default due to security concerns. You can enable flash player for IE in Windows Server 2016 by following steps

1. Open a command line windows and run following command

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

   

2. Reboot, after reboot open adobe flash player official test page with IE to check if flash player is enabled