I've made simple WinForms application, single purpose of which is showing popup messages. Basically, it is minimized form with hidden taskbar icon, and NotifyIcon.
Everything works ok, but I don't like it being placed in Apps category in Task Manager, not Background Processes. So, what is a difference between background process and app in terms of VS project settings, class usages etc?
Task manager detection of "Applications" depends on the process having a top-level window.
You can avoid this, and be detected as a "Background Process" by not having a top-level window. Since notification icons need a window, you can't get rid of it entirely, but you can set TopLevel = false.
This will probably also remove it from the taskbar.