By locking down the OS. Windows S Mode becoming the standard, with features locked out on other versions. That kind of thing.
Microsoft may be dumbing Windows down but there is zero chance they ever dumb it down enough so that it's not the premiere gaming platform. Why would they, to force people to buy Xboxes? Xboxes that are essentially... PCs?
It is entirely possible. Google and Apple both have higher gaming revenues (by a considerable margin) than Steam, without producing or publishing games. How? They are the only provider of the content on their respective platforms.
You seem to have forgotten that both Apple and Google are currently the subject of multiple lawsuits in multiple countries regarding their walled gardens. Microsoft has already had one ride on the antitrust wagon and unsurprisingly they're not interested in another.
But you also seem to have forgotten that Microsoft recently did try to compete with an established contender, when they bought out Mixer to try to fight Twitch. In case you need a reminder of how that went, the answer is
not Microsoft's way. After throwing money into that particular pit, I somehow doubt their shareholders will let them try the same thing against a competitor in a different space - a competitor that's arguably far more formidable.
I agree with
@Count von Schwalbe that it's possible although not probable as you would be sacrificing some potential sale numbers at the start. If you look at Blizzards Battlent launcher, the vast majority of their games are exclusive there. They peaked at 45m active monthly users on battlenet after the latest WoW expansion but typically are around 30m active monthly users. That number will increase again once Diablo IV launches. If they could add some more exclusive tent pole IPs like Fallout, DOOM, Skyrim, CoD to Battlenet, you can start pushing closer to STEAM 130m active monthly users.
And you'll find that nobody who uses the Battle.net launcher uses it for any reason other than Blizzard games require it. Number of users is utterly irrelevant if those users don't engage with your platform any more than they have to. Steam isn't just a games launcher, it's an entire ecosystem and a storefront that has become second nature to its users over many years, and there is zero opportunity to shift users away from it without adding something that's significantly better - and so far, not one of Steam's so-called "competitors" has managed that. Even Epic, who's
literally giving things away for free, has so far been unable to dent Steam's market dominance. By implication that means that most gamers see Steam as better than free, and in a capitalist world that is an unassailable lead.
The possibility of Microsoft locking down Windows is what led gaben to pivot Valve from game developer to Linux developer. (Remember that he's a former 'softy and had a front row seat for early iterations of Embrace/Extend/Extinguish.) All of Steam's hardware, back to the original Steam Machine, was built to be free of the Windows ecosystem. Proton has done marvelous work in making Windows-oriented code run on Linux.
Here's an article from ten years ago, where gaben talks about the necessity of getting away from dependence on Windows.
https://kotaku.com/gabe-newell-wants-to-support-linux-because-windows-8-i-5929067
Right on cue the neckbeards crawl out from their basements to proclaim Gaben as their lord and saviour because HE DID SOMETHING FOR LINUX THAT ONE TIME.
Valve doesn't actually give a s**t about Linux. You know why? Because Linux doesn't make them money, it allows the hardware they build to make them money. The first piece of hardware they tried to make Proton a thing with was Steam Machines, and does anyone remember those? No, and guess why? Because Valve killed them
because they didn't make money. If the Steam Deck fails to hit revenue targets (which I expect to be the case because it's not a particularly useful or revolutionary piece of tech, just a cool one) then Valve will kill it too, and where does that leave Proton? Waiting and hoping for Valve to build another piece of hardware to justify its existence?
Valve is a company that exists to make money. It is
not an altruistic friend of Linux users, not matter how much said users may delude themselves.