See the box at the top of article showing difference between monopoly, monopsony, oligopoly, oligopsony.

A monopsony would mean the buyer gets to dictate all the terms, and the seller has to sell at very low price. In this case, TSMC has something very valuable, and Apple is paying a considerable amount (presumably, I haven’t seen real numbers) to the seller to make sure no one else gets it.

In fact, TSMC is a monopoly, the only seller of a much sought after product.