They've been working on Linux support since at least around the time that Microsoft introduced the Windows Store... so for the last twelve years or so.
And, man, a couple of months ago I figured out how to run Steam as a separate user on my Xorg system. Not-at-all-coincidentally, I haven't booted into Windows in a couple of months. Not every game runs [0], but nearly every game in my library does.
I'm really gladdened by the effort put in to making this work.
[0] Aside from the obvious ones with worryingly-intrusive kernel-level anticheat, sometimes there are weird failures like Highfleet just detonating on startup.