Unity 2020.3.15f2: Choose between VR and Desktop at launch

Question

Lots of games have options for launching in VR or Desktop modes, either through steam launch options ("Play game", or "Play game in VR") or command line flags (-vrmode none, --no-vr) at least from a user perspective. Phasmophobia, which was developed with Unity (engine version unknown) uses the -vrmode none option to force the desktop version of the game. I'm guessing this was in the 2019 version of unity, as that still supported the dev SKD options under Project Settings -> Player -> XR. However with the newer 2020 LTS version of unity, using the OpenXR Package, I don't see an equivalent.

I'd like to give a command line option to my game to launch in either VR mode or Desktop mode, then stay in that mode for the game session. Is there a way to do this with the OpenXR package?

Engine: Unity 2020.3.15f2
Template: Universal Render Pipeline
XR Interaction Toolkit Package: 1.0.0-pre.5 [Preview]
XR Plugin Management: 4.0.7

Only OpenXR is selected in XR Plug-In Management. This is a bare-bones project with an XR rig and a single intractable for testing.

Answer 1

After more work and communicating with people, I managed to figure this out myself.

For other people who find this post, here is the solution for VR and non-VR in a single build.

Note that this will start your game in 2D, NOT VR. After it loads past the unity splash screen, it will switch to VR.

You need to create an empty game object in your scene (you do not have to switch scenes for this to work) and attach the below script to it. After this, build your game and launch the game with the "--enable-vr" flag after the game.exe. In a Windows Shortcut, this looks like "C:\Path\To\Game.exe" --enable-vr

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.XR.Management;
 
public class VRSwitcher : MonoBehaviour
{
    public void Awake()
    {
        StartCoroutine(StartXRCoroutine());
    }
 
    // This function checks out startup arguments to see if we want VR
    // To do this, create a desktop shortcut and add the arg at the end.
    // Example: "C:\Path\To\Game.exe" --enable-vr
    private static bool GetArg(string name)
    {
        var args = System.Environment.GetCommandLineArgs();
        for (int i = 0; i < args.Length; i++)
        {
            Debug.Log($"Arg {i}: {args[i]}");
            if (args[i] == name)
            {
                return true;
            }
        }
        return false;
    }
    // From unity docs
    // https://docs.unity3d.com/Packages/[email protected]/manual/EndUser.html
    public IEnumerator StartXRCoroutine()
    {
        var enableVRArg = "--enable-vr";
 
        // Only run the code block when we want VR
        Debug.Log("Looking if VR should enable");
        if (GetArg(enableVRArg))
        {
            Debug.Log("Initializing XR...");
            yield return XRGeneralSettings.Instance.Manager.InitializeLoader();
 
            if (XRGeneralSettings.Instance.Manager.activeLoader == null)
            {
                Debug.LogError("Initializing XR Failed. Check Editor or Player log for details.");
            }
            else
            {
                Debug.Log("Starting XR...");
                XRGeneralSettings.Instance.Manager.StartSubsystems();
            }
        }
        else
        {
            Debug.Log("Did not find VR arg, starting in 2D");
        }
    }
}

I hope this helps someone