Setting a camera to have a green background for chromakeying in a different app?

Sorry if this is a stupid question.

I’m wanting to make something in the Unreal Engine and use it as an overlay in OBS. I would love to be able to render using an alpha to make the game transparent but I’m guessing that this isn’t a thing? The obvious alternative would be to set the engine to render an green background but I can’t seem to find the options for doing this. I was kinda hoping there would be an option in the camera settings to choose a background colour but I had no luck when looking.

Is there an easy way to do this? I suppose the alternative is to make a sphere or a plane and add a green texture to it but I’m guessing there will be some issues with lighting? Any help with this would be really appreciated. Everything I’ve found in google refers to using unreal for importing greenscreen elements rather than output them.