All those drain cleaners didn’t work. Pulling the stopper out and cleaning the gunk off a paper towel worked.

I recommend nitrile gloves. Don’t run the tap when you have the lever screw open, water will leak out of there. You can use an old toothbrush to reach down the drain pipe and pull up more gunk. After, I filled the sink up with hot water then drained in one go. Don’t know if it sanitizes exactly but I think it helps, cut down on the smell anyway.