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.
On your last point, there’s also Flatpak which is available right from the baked in software center… That’s not without its issues too, but they’ve been an overall smooth experience for me so far