According to these new numbers from Valve, the Linux customer base is up to 1.96%, or a 0.52% jump over June! That’s a huge jump with normally just moving 0.1% or so in either direction most months… It’s also near an all-time high on a percentage basis going back to the early days of Steam on Linux when it had around a 2% marketshare but at that time the Steam customer size in absolute numbers was much smaller a decade ago than it is now. So if the percentage numbers are accurate, this is likely the largest in absolute terms that the Linux gaming marketshare has ever been.
Data from Valve: https://store.steampowered.com/hwsurvey/Steam-Hardware-Software-Survey-Welcome-to-Steam?platform=combined
Less than that though they are a large slice.
Most Windows and practically all Mac instances are preinstalled by the hardware vendor. There are very few companies selling preinstalled Linux gaming machines other than the Steam Deck. I expect they might be a majority of new Linux steam users for some time as they are by far the lowest entry cost in terms of hardware, prerequisite technical knowledge and time.
Many gamers who dabble with Linux are still taking the path of least resistance and dual booting for gaming. Linux first people like myself will continue to grow in number but as long as it is a DIY thing realistically we will always be a few percent at best as most people want a simpler out of box gaming experience.