It peaked at 4.05% in March. The last 2 months it went just below 4% as the Unknown category increased. For June the reverse happened, so 4.04% seems to be the real current share of Linux on Desktop as desktop clients were read properly/werent spoofed.
Based on a world population of 8 billion, that would be roughly 0.00000000000000125% of a person. And is also not even representable in a 64 bit float so I had to do this math in my head (Calculator just says 0)