The idea is that the PC sound comes out thru the green speaker socket on the pc into the mixer, can be mixed with the mic sound and the output is fed into PC mic in socket. With OBS running this following is set up in the Audio and Audio properties for each video that you need to play.
In Zoom the sound in (Mic) is set to : Line In at Rear Panel Blue. The sound out – to hear other ppl on the zoom call is set to (in my case) my Samsung TV. The disadvantage of this setup is you can’t hear the video sound (to avoid feedback). So with my mixer I have headphones coming out of the mixer headphones socket.
Audio properties for each media item (video)