A typical pattern is to have two apps. You can't really do this. as services run in a different window station than the logged in user, so you can't have a system tray icon for those users. This is from the Microsoft docs https://learn.microsoft.com/en-us/dotnet/framework/windows-services/introduction-to-windows-service-applications:
Windows Service applications run in a different window station than
the interactive station of the logged-on user. A window station is a
secure object that contains a Clipboard, a set of global atoms, and a
group of desktop objects. Because the station of the Windows service
is not an interactive station, dialog boxes raised from within a
Windows service application will not be seen and may cause your
program to stop responding. Similarly, error messages should be logged
in the Windows event log rather than raised in the user interface.
The Windows service classes supported by the .NET Framework do not
support interaction with interactive stations, that is, the logged-on
user. The .NET Framework also does not include classes that represent
stations and desktops. If your Windows service must interact with
other stations, you will need to access the unmanaged Windows API. For
more information, see the Windows SDK documentation.
The interaction of the Windows service with the user or other stations
must be carefully designed to include scenarios such as there being no
logged on user, or the user having an unexpected set of desktop
objects. In some cases, it may be more appropriate to write a Windows
application that runs under the control of the user.
Here are a couple of links about how to write to the system tray I found on internet and other post. You'll need another application to interface with the service, since the service can't directly have an icon in the system tray for windows..
How can I make a .NET Windows Forms application that only runs in the System Tray?
and
http://msdotnetsupport.blogspot.com/2008/02/cnet-application-windows-system-tray.html
Way to communicate with the windows service could be as follows: