Same issue here. When I unclicked the initialized XR during startup and it renders the component in a window. But when I checked that box and deploy again, nothing was rendered after opening the app. Not even working on the example scene. I worked with MRTK2.8.3 Unity 2020.3.11f1 and VS2022.

Everything was fine when I worked with MRTK3 on Unity2022.3.58f1, I don't know what's happening to MRTK2.8