> Other than obvious things such as "Amazon products"..., in which case every manufacturer or retailer is a monopoly in their own products.
The way this argument is normally presented is somewhat intentionally obtuse. Obviously Nike has a monopoly on Nike shoes, but "Nike shoes" isn't any kind of sensible market definition because you go to a shoe store and there are a dozen brands of shoes that are all pretty fungible with each other.
But then you get into something like "GM-compatible brake pads" and that is a sensible market definition, because if you have a GM car and you need new brake pads, they need to be compatible with your car. But you'll also notice that this isn't the same thing as GM-brand brake pads. You could get GM-compatible brake pads from a variety of OEMs that are all compatible with your GM vehicle.
Or, it could be the case that only GM makes GM-compatible brake pads. In which case they would have a monopoly in that market. Not because it's a monopoly on their brand of brake pads, but because it's a monopoly on any brand of brake pads compatible with that brand of cars -- which is something else entirely.
Notice that they don't even have to be the same company. If you have a Studebaker, the Studebaker Corporation is no more, and you may have trouble finding parts. It may even be the case that some independent third party has a monopoly on some such parts, even though it's a monopoly on parts for one specific brand of car.