By your definition, lets imagine a world where Amazon had 100% of the market and there were no other competitors, even if it happened naturally, without malicious intent, they wouldn’t be a monopoly? Come on.

I dont see 'has to act a specific way' in any definitions of monopoly. A monopoly isnt about being evil, or 'actions taken to make such an outsized market power' even if thats often part of the result, but just describes their position in the field.

This isn’t about how a company got there, it’s about where they currently are. Steam may not have crushed competitors aggressively like Disney or Nintendo, but its market dominance and control over PC game distribution still fits the textbook definition of a monopoly.

Steam has ~79.5% of the PC gaming market, I’m one of their customers and love their service, but that doesnt change that “monopoly”fits them.