Yes, you can, and yes, among the group of people represented on HN, I have no doubt that a fair number do use it this way.....but how typical is that? How often does the average steam deck owner use it as a desktop? How often does the average user leave the steam launcher? How often does the average user think of it as anything other than a gaming console?

If all you care about is some very technical sense of "how many linux desktop environments are installed in the world", then none of these questions matter. But if the reason one is interested in the "Linux Desktop market share" is some level of interest in how people are using desktop computers, and when/if they are choosing them over competing OSs like Windows and MacOS, then these questions matter a lot. My guess is that 90% of SteamDeck owners don't think about the fact that it is Linux, barely every leave the steam launcher, and were they to be looking at getting a new desktop computer, their SteamDeck experience would not make them consider a linux distro vs. Windows or MacOS.

In case it matters, I think more people should be running Linux than do, I think people over-estimate the difficulty of switching. I want the steam deck and SteamOS to be a gateway for people to switch in more contexts....I'm just skeptical that it's actually doing that more than a trivial amount.