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.
You can “sideload” apps outside the google store.
For example I’ve been using myinsta instead of IG. It was very easy to download and install.