> I would guess that users of the Steam machine would mostly be as locked-in to Steam purchases as PS5 users are to PS Store purchases.

[pirate flag emoji].

Games from sources other than Steam are a bit more fiddly to get going, but it's far from impossible. Like Valve says, it's your computer.

The steam machine is just a regular Linux PC, you can install anything you want on it.

I have the Deck and I mostly use it to emulate Switch & PS2 games.

Steam machine is not locked into the steam client. You can install whatever you want.