Hello @thezoeyteh
I’ve been doing the same stuff for around 8 months now. And came pretty close of making it real.
You can see every steps i went through here : Trying to get an HDRP portal to work on VR
You can also download the project on the gitlab link provided. (It work perfectly in desktop mode and is seamless)
There is only one problem : The render pipelines URP and HDRP both doesn’t support VR on the Shader graph node ‘ScreenPosition’. Which mean we cannot really create a shader to project the portal picture at the right position.
Fortunately few hours ago I successfully opened an issue with the Unity team here : Unity Issue Tracker - [Shadergraph] ScreenPosition node does not work when XR is active
I invite you to upvote this issue and to share it, because once this problem will be fixed we will be able to make portals in vr properly. So the more people upvote this, the faster we will be able to make portals/ mirrors or any effect based on render textures.