Monopoly, noun: the exclusive possession or control of the supply of or trade in a commodity or service.
Imo this does not apply to Steam. They do not have an exclusive possession or control of the PC gaming market. As is proven in the rest of this thread by just about everyone, there are other online game stores/launchers besides Steam. Literally no one is forcing you to use Steam (because then it would be considered a monopoly), when Epic, GoG, Uplay, Origin, and Rockstar Launchers all exist.
Again, like it was said elsewhere in this thread, they’ve just crushed the competition so completely that it feels like they have a monopoly.