How much of that unknown is linux tho? I feel like linux computers are most likely to be unidentifiable (ignore the 5 ppl who use templeOS and freeBSD)

Unknown is Windows. If I recall correctly, there was a Windows update (in May or June, I believe) that caused it to stop registering as Windows with the site. A subsequent update fixed the problem. That’s why if you look at another chart on the site, you’ll see an equivalent increase in Unknown as Windows decreases during that time period.

This isn’t the whole reason, and likely only a small fraction of it. There are a whole lot of other OSes that don’t fit into these categories, or that simply refuse (on purpose) to share their OS type. That wouldn’t be Windows.