This is interesting for a couple of reasons. One is that this is about as much market share as Mac ever had at its peak, and almost twice as much as it has currently. Another is that, if you click the link for the site's Steam Linux Data Tracker, you can see that English-only Linux market share (a crude way of filtering out the ebbs and flows of Chinese players on largely-identical hardware and operating systems) is more than 6%, up from under 2% just 5 years ago. A lot of people are unhappy with Windows in general, and especially 11, and Windows 10 is about to force the issue in just a few months as it loses official support. I have a friend whose computer is still in decent shape for gaming but with TPM settings that don't meet the minimum spec for Windows 11; at some point, he'll lose compatibility and have to throw out an otherwise perfectly functional machine, so it's good that some other OS is shaping up to be a good enough option for many people.
This has been an upward trend since slightly before the release of the Steam Deck, as you can see on the graphs, and I've come across YouTube videos from both James Lee Animations and PewDiePie about how they got to be so sick of Windows (and Adobe) they both switched to Linux with middle fingers raised at their old workflows. Folks like them making videos like that can have real effects on the market. Linux has been my daily driver for gaming for about 8 years now, and it's matured so much in that time that I've hardly booted to my Windows partition for any reason. It's not perfect, but if I'm choosing between the quirks that Linux has by accident and the deficiencies that are in Windows on purpose, I'll take LInux every time, and it seems like more people are coming to that same conclusion.
No doubt the biggest remaining frontier is live service gaming with kernel level anti-cheat, but if Linux becomes a larger user base, as it's doing right now, the developers making those games will have to solve that problem to reach that addressable market, and everybody wins.
