The OP link — https://gs.statcounter.com/os-market-share//
https://statcounter.com/how-it-works/
https://gs.statcounter.com/factsheet
This SAAS — https://statcounter.com/ — strictly uses websites/browsers for all of it’s stats. Since the SAAS works by website owners placing a bit of code on their page, statcounter scrapes the data from all their SAAS customers and combines it to put out their overall stats like the OP OS usage subject.
As far as IDing individuals, they use cookies. If you clear your cookies and visit again, you’ll get counted twice. Think of it like polling. They’re using stats from a small percent of WWW users. Is it 100% accurate? No, just like polling isn’t.
“Since the SAAS works by website owners placing a bit of code on their page.”
Yep, I understand. But how many domains actually do that and contribute? 25%? Pretty hard to take polling from 25% and determine a guess what the true 100% would be. I think in all this they are just Guesstimating the numbers of Linux users. There is still a whole lot of room for error. Like I mentioned earlier, The numbers I see here are the same numbers I remember seeing 15 years ago. There is no way they could still be running along those same low percentages now. Linux has been exploding because of the recent MS issues.