Sealing gap(s) around cabinet pipe penetrations
I'm wondering if I can seal those gaps if that might eliminate the odor?


Well, yes, if the odor is coming through the gaps. You could try to stuff something like fabric or cotton in there as a temporary seal, and seeing if it reduces the smell.

I think it would be easier to solve your issue if you could definitively identify the source of the smell first. It could be coming from your garbage disposal, mold on walls, the trash bin, or other things.