Well if you're counting, I've got one.

No, definitely not but getting there! Last year despite slow production ramp up, about one million were sold. Source: a SteamOS developer on a KDE conference in autumn.

This year a financial analyst company predicted an additional two million until the end of this year but that was before the OLED announcement. Valve then recently said "millions". So I guess 3 million may be a somewhat conservative estimate now that the OLED model is out. 4 million if we're generous. It'll take a while until 10 million are reached, if they'll be reached at all. My memory is a bit foggy but I think Valve people said that the Steam Deck was intended to launch earlier but the Covid semiconductor crisis delayed the announcement. My guess is that at least a Steam Deck Lite will be announced first but the overall performance will stay about the same, so that could drive sales a bit before the eventual successor comes out.

It's not about Deck alone. Supporting Deck, means supporting all Linux machines and everyone else with controller.