Here is the graph showing Linux market share over the last two years according to five different sources (the Steam Hardware & Software Survey, the US Gov website, w3counter, statcounter, and Cloudflare):
Please note that CloudFlare and StatCounter data are updated daily, whereas all other sources are updated monthly. Though each data source uses very different methodologies, this graph should be able to tell us about general trends over a medium length of time.
You can find more data and a description of the handling of each source on this page. Please note that part of it is reserved for paying subscribers as aggregating the data takes some time, and donations help me work on more features (such as by-country graphs and longer history) and, more generally, to run the website.
CloudFlare
CouldFlare data uses the number of HTTP requests broken down by Operating System. You can explore the data for yourself here.
I have decided to set "Device type" to "Desktop" as I'm only interested in desktop marketshare, and I have kept "Bot class" empty as "Likely human" lowers the Linux marketshare significantly, and I'm worried that Linux users are considered more likely bots.
The data is continuously updated, which is great; however, it's provided as a percentage of HTTP requests each day, and to get the monthly value, I average them. I have found this to be rather accurate, but it does not account for which days have more traffic. Therefore, the number you see might differ from CloudFlare's own tally.
If necessary, we could filter the requests by country and have some more detailed geographical data, but I have not worked on that yet.
Statcounter
Statcounter publishes its methodology here and here, and you can see the data for yourself here. Again, I'm only interested in desktop market share, so I filter by that type of device.
I believe this to be the second-largest source of data after CloudFlare, as they claim to have had a sample of 5.3 billion page views in 2022. Of course, that might not be representative of the larger population.