The Oculus PC app is auto opened when I open the Steam app even if I'm just wanting to run non VR games. If I close the Oculus app then it closes Steam with it. Is there way just to use the PC Oculus app only when needed for VR only? I have several games that are non VR and wish not to have a non related gaming app forces itself open when playing flat screen games.
Yes, there is. It's called the program Virtual Desktop. If you're using Oculus Link or Air Link then the Oculus desktop app needs to be running, because that's how your HMD is connecting to your computer. Closing the app cuts the connection to your computer.
Regardless of how you do it or what HMD you use... I believe you will always need the a VR app running in order to play flat screen games while in VR. Be it Steam VR, Oculus Home (and thus the desktop app), Virtual Desktop (which is a non-intrusive streamer app on your PC and runs the main app on your Quest) you need something to act as the VR interface. For example, right now I am sitting in a movie theater while posting this replay, thanks to Virtual desktop. I'm then planning on playing Final Fantasy XIV for a while, which is a flat screen game. I'll be using a controller, since I can't really see the keyboard right now.
EDIT: I am assuming you are wanting to play a flat screen game while using your Quest, Quest 2, or Rift. If you're not trying to play the flat screen game while in VR, then the Oculus app shouldn't be launching when you start up Steam.