So I finally figured it out. I have no idea how you did this with a lerp3, so here is a screenshot of how I got mine working.
In the level I modified my test code to toggle the render depth passing in 1, 2, and 3 to index the different highlights. The cube on the left is index 0, that’s why it looks normal.
I could pass the lerp4 directly to emissive color, but that results in the highlighting rendering through walls. So I set up the scene depth / custom depth if check to get it looking like your result. Found that info in this very helpful basic tutorial on custom depth.
