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.
So your definition for “desktop” is if it’s an x86 compatible architecture? Seems pretty random to me. Btw, there are x86 android device. IMO a desktop is something on the top of a desk to do typical “office work”. PCs, Macs, Laptops, etc. but calling a SteamDeck game console “Desktop” is pretty dishonest I think.