A modified SteamVR plugin that can be injected into Non-VR enabled Unity projects for VR rendering and VR input/interaction. Modified for IL2CPP with Melonloader. Needs SteamXR_Melon. This thing was made for Unity 2022.3.16f1
You need to replace the memory offset in the PluginImporter/GetLoadPluginFunction() with the memory offset of FindAndLoadUnityPlugin from UnityPlayer.DLL (in your game install folder) for the exact Unity version your game is using.
var loadLibraryAddress = module.BaseAddress + >>> 0x786D00 <<<
I recommend using Ghidra or IDA to get the mem address.
PDB files for the il2cpp UnityPlayer ship with the Unity editor and can be found under Editor\Data\PlaybackEngines\windowsstandalonesupport\Variations\win64_nondevelopment_il2cpp You need to have Il2CPP support enabled in the given Unity install for them to appear.
Call SteamVR.Initialize(false) before the game loads. Call MelonXR.Initialize() after that Add SteamVR_Camera on the main player character. You may need to tweak the Expand() function in SteamVR_Camera depending on the needs of your game. For rendering UI look at Eusth's VRGIN approach or at GTFO VR if you're ok with just using SteamVR_Overlay for it.