Recursive RenderTextures/ Feedback effect ala Portal?

In Valves’ Portal, if you face 2 portals a certain way towards each other, a feedback-like effect is created from the portals staring into themselves. Using render textures to try and mimick this, my render textures are black where portals should be. I’m using URP, if that makes a difference. Please help me, anyone… it’s been 3 weeks and I cannot recreate this effect for the life of me, and I cannot proceed without this effect working.

Have you tried adding cameras to the portals? I mean put a camera to each portal and set the texture of the portal as a camera or something.

Here’s something of sorts:

I figured something out: I disable the camera in the inspector but not the gameobject. I place the camera where the black spots should be in the portal, and I manually render there first in code before rendering the original spot. I got the idea from here.

This still creates a black spot/LSD visuals, but if you want to solve that, then the solution is the same: for a further recursion, place the camera first where that spot is, next where that first spot will be, then in it’s original position. 4 recursions? place it in the 4th spot, render, then the 3rd, render, then the second, render, then the original, then render that.

So on and so forth for 5-6-7-however many recursions you need, or whatever.