I see that a question about "owning" chametz during pesach via stocks has been answered here: https://www.yeshiva.co/midrash/51525 However the Mishnah and Mishneh Torah both specify that it is prohibited to benefit from chametz during Pesach as well. Would owning stock in a company that sells chametz present a problem in this context?

The previous response which you mentioned already related and precisely answered your question, for everyone knows that it's prohibited to benefit from chametz during Pesach, and nevertheless, the poskim (halachic authorities) generally allow holding shares in such companies, for the reasons mentioned.