I really think Valve have become the de-facto owners of the “don’t be evil” motto nowadays, even if they don’t advertise themselves as such.
It’s not just factually wrong to call them a monopoly, it’s uncharitable given that they are not engaging in anticompetitive practices despite being in a position (and arguably having the right) to do so.
It's also so clear to me in retrospect how long they've been building up to something like this. Investing in Wine and developing proton to make running Windows games on Linux as frictionless as possible, dipping their toes in hardware with much less ambitious projects like the Steam link and the controller for it so that they weren't going in without any experience as a company dealing with physical products...I can't imagine that this would have been able to pull for for most companies due to how much they had to be willing to invest in long-term endeavors that couldn't be guaranteed to succeed. I don't think it's that much of an exaggeration to say that they might have single-handedly lifted up Linux gaming to the point where I'll never end up using Windows on a personal machine again, and that's because they put so much time and effort into the tooling for running the games independent of their distribution network. At this point, I probably would have been willing to forgive them for releasing the Steam Deck as a locked-down device, but instead they went ahead the made it pretty much indistinguishable from my laptop and desktop in terms of how much I can change or remove things. There have been so many discussions about whether the App Store should be considered a monopoly or not on iOS, and if there's not consensus on that, I can't even fathom how someone could make the argument that Steam is.