Hey
@Ben vera - DAWs don't play well with Macs/OBS out of the box unfortunately. The best solution I've found is Loopback. It costs $99 but has a free trial so you can try it out beforehand. You can manage all of your inputs/outputs on Loopback directly. Here's the link:
https://rogueamoeba.com/loopback/
To integrate with OBS, make sure Loopback is running and set your "Desktop Audio Input" in your OBS preferences to "Loopback Audio Device".
I know others have had success using Soundflower to accomplish a similar result, which I believe is a free plugin. I've found Loopback to be well worth the cost and not nearly as buggy. Let me know if this works for you or if you still have issues.