In the three years since its release, the Steam Deck has outsold all of its competitors, including the ASUS ROG Ally, Lenovo Legion Go, and MSI Claw combined. Valve's portable console has sold an estimated 3.7 to 4 million units, according to The Verge.
This was calculated by the analytical company IDC. In total, over the past 3 years, about 6 million devices have been sold in the market of portable game consoles on Windows and SteamOS. More than half of this number is accounted for by sales of the Steam Deck.
It is worth noting that IDC does not include Chinese handheld consoles such as GPD, Ayaneo, and OneXPlayer. However, it is likely that their market share is not very large.
However, Steam Deck is increasingly struggling with new releases, especially those running Unreal Engine 5. At the same time, Valve has repeatedly stated that it does not plan to release Steam Deck 2 in the near future. The company intends to wait until it becomes possible to significantly increase performance without compromising the autonomy of the device.