Recently, the NetMarketShare website and the Steam Hardware Survey showed the Linux share was rising but it appears both have now calmed down.
For NetMarketShare, something pretty big happened over the last few months. Back in March the Linux share they recorded was only 1.36%, and then it quickly rocketed upwards to 3.61% in June after multiple months of rising. The kind of rise you can't easily just write-off since it continued happening. No one really knows what caused it, possibly a ton more people working from home and not attached to their corporate Windows workstation. Now though, it seems to be levelling out as July's figure now shows it as 3.57%. Considering more people are being told to go back to work, perhaps it was as a result of COVID19. Across this whole time though, it's worth noting StatCounter which also tracks it has hardly moved much during it. So you may want to press X to doubt on it.
It's a tough thing to truly measure though, considering they all tend to rely on visitors browsing a specific set of included websites. They capture things like your browser string which can often be faked, but they're still about the best we have for an overall picture of any possible trends. One thing is for certain though: not a lot has changed overall.
As for the Steam Hardware Survey, it rose from 0.83% back in February up to 0.91% in May but it also has been slowly trickling down with it now sitting at 0.86% as of July's numbers. At least when looking over the past ~2 years, it's still trending upwards slightly overall. We're tracking it on our dedicated Steam Tracker page here, in case you haven't seen that before. We also recently added the ability to filter to specific year/months on our Steam Tracker, to allow for fine-tuning and adding more historic data.