Steam does not have a monopoly by any actual definition of monopoly, though. A) Mobile gaming makes up the most of all video gaming revenue. B) On PC the most revenue is made by games that aren’t even on Steam in the first place (Minecraft, Fortnite, Roblox). Steam’s 2023 revenue has been estimated to be around 8.6bn USD out of 45bn USD of PC gaming revenue. That’s barely a 5th of the market power. By no account this can be actually considered to be a monopoly.