If you want to prevent server manager from running every time a user logs into a server you might be tempted to down the route of a GPO.
There is a specific GPO for this and its a good idea (here for how to do that,) to set it as it will prevent a non-privileged user from loading server manager not just a log in but at any time. However with just this GPO set users to get the following error every time they log in.
To get rid this open an elevated CMD window and issue the following:
schtasks.exe /change /tn "\Microsoft\Windows\Server Manager\ServerManager" /disable
This will disable server manager at start up and prevent this message. This path is correct for Windows 2016. It may be slightly different in other server versions (I'm pretty sure it is).
You can get the correct path from Task Scheduler.