How to extract elemental bismuth from pepto bismol?
I'm not sure you did do the experiment wrong. I performed this experiment and it closely matched this video which had a light yellow liquid and foam.

Here are my results



I filtered it a couple more times to remove more foam. Then added the aluminum foil.



This is what I got at the end before I filtered the liquid out at the end.

In the end I was able to extract 6.2 grams of bismuth powder from 67 tablets of pepto (a bit less than the theoretical ~10 grams I was hoping to get).