And just in case I will be away for today, here is sort of how I separated Foreground and Background; I used 2 Scenes, Foreground (Christmas Cat and Lights, for instance) has Transparent checked:

The other Scene (start with Full Copy, to the right of the Scene name) has Transparent un-checked and all foreground elements (or the Collections that they are in) set to Hold Out (Filter if that doesn’t show up in the Outliner):

I hope that is sort of clear 😉