How is the automatic background layer created?

Hello

I’m having shadow issues… as blender seems to be good at… but I realized that the “background” layer is automatically rendering the shadow catcher with object shadows without the models rendering, Nice…
I can do this in a separate project file, but I want to put it on a separate layer… but In my haste, I deleted the background layer and for the life of me… I can’t figure out how the background layer is / was created.
When you select the background layer (in my pervious version) the modifiers go away, no modifier menu, no particle menu, no physics menu… and only the shadows and shadow catcher render… How does it create this in the same project which has the foreground layer?
What I mean is… I want to render all my elements from one project, So I try to create a shadow render pass… so I go to the object panel, and uncheck the camera option from the visibility menu… it works great… I get a shadow with no object… great, but then the foreground layer doesn’t work… because the objects have the visible unchecked… I thought it would be different settings in the different layers, but not that check box… it stays the same in my new created layers…
So what’s the mystery about the background layer that blender automatically creates? And how do I recreate it?? Can’t find any info or anything on the web…

Thanks in advance for any help someone may have.

I hope this makes sense… and I hope someone says this is a newbie issue and that there is a dead simple way to fix or do this…

thanks

Those operations are done with Collections (right click it for options). Two collections and two layers are created. In foreground layer, background collection is set as holdout, the shadow catcher. In background layer, foreground collection is set as indirect only, the objects. Both makes objects invisible but Indirect Only still cast shadows and reflections, Holdout exclude an collection completly and if is in front another object, from other collection, makes a hole.