Not sure about live, but if you are doing a recording to post later, you can chroma-key it out or even just make a mask in your post production editing.

Or if you want to get a little janky, you could make a scene in OBS and record it there. Sounds hard, is really not. You make a scene with whatever you want your background to be, then create a new source that would be video capture and you can arrange them on the screen in any way you want.

This sounds like a viable solution that I’d be happy to walk you through, or even set up for you if you can’t find anything easier. Just a suggestion.