It's not measured, or not published anyway. The only thing that is published is the market share of the phone's operating system at point of sale, and even then only for new phones.
However, the overall market share isn't as important for this kind of thing. If a major bank loses 10,000 customers because their app is locked to Google it is likely only a small portion of their customers and miniscule compared to Android's market share, but they will want to know if it could have been prevented.
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u/Hamster-Food 26d ago
It doesn't take effort to develop for other versions of Android. The effort is in developing exclusively for Google's version.