Native Cross Platform Loading Screen?

Hi, I am trying to reproduce this scene loader in a project with URP. As URP treats Graphics.Blit different, I am trying to use the Camera stacking functionality, so one camera renders the scene and then fades to black with a PP Volume, and the other renders the loading cube. However, even though I am using Single Pass Rendering, the base camera is only rendered to one eye. Has anyone solved this?

I've looked in the threads for alternatives and one could be using compositor layers, but it seems that now only works with the Oculus and SteamVR plugins and I'd like to avoid using them. In this thread, they have asked about it, but there hasn't been any response for some time.

Anyone has achieved a nice loading screen that works with URP?