post comment : https://blogs.technet.microsoft.com/rmilne/2014/05/30/how-to-hide-server-manager-at-logon/

gistfile1.txt

If you'd like to set this properly in the Registry via cmd/bat, or PowerShell, be sure to specify the key is in HLKM, not HKCU.
Get-Item HKCU:\Software\Microsoft\ServerManager may succeed, but the other 2 fail if aimed at the Current_User hive.

Presuming what you'd like is for ServerManager to NOT auto open at logon, the following 1-liner (PowerShell) will test if the registry value should be updated, and then update the proper key/value:

if ((Get-ItemProperty -Path HKLM:\Software\Microsoft\ServerManager -Name DoNotOpenServerManagerAtLogon).DoNotOpenServerManagerAtLogon -ne 0) { New-ItemProperty -Path HKLM:\Software\Microsoft\ServerManager -Name DoNotOpenServerManagerAtLogon -PropertyType DWORD -Value '0x1' –Force }