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.
This is clearly a statistic about PCs, otherwise the share wouldnt be ~73% windows. So the decline of the desktop PC doesnt really matter here
The people who are more likely to retain a PC and not just use a phone, are more likely to be tech literate power users.
This selects against casual windows users, and selects for hardcore Linux users