OS market share: https://gs.statcounter.com/os-market-share is a place a lot of linux users stare at to check how close we are to "The Year of the Linux Desktop" which has become a meme. However, across all platforms, but mobile and desktop, Android has the most users, with iOS in 3rd place.
Its interesting to think about that more people have cell phones (or pocket computers) than people who have desktop PCs. In fact, most people may have only have school work to thank for any desktop experience at all. Such as school issued laptops or a laptop purchased specifically for college and that may be their only desktop user experience.
If only the mobile market is taken into account, with other platforms excluded:
Mobile Operating System Market Share Worldwide - April 2024
Android 70.87%
iOS 28.39%
Developers should think about whether iOS is actually worth supporting given the 30% cut they take. Is the Apple market worth it? Sometimes the answer is yes, but only when the Android market is too crowded to compete. Even if Apple support is worthwhile without an overcrowded Android market, an Android first iOS later approach would be the most worthwhile, that way its the value of the Apple market that is being judged rather than whether your app has a product market fit (and its less expensive for the apps launch that way).
One might see this and think this means "Google Play market vs Apple market", but plenty of phones ship with their manufacturers app store, such as The Samsung Galaxy Store. Not only that, but you can ship an Android phone too. Graphene OS is a common one that gets thrown around, but really you can go to the Android Open Source Project and compile your own. For example, despite just being Android 14, Xiaomi calls their custom ROM, "HyperOS"
Most Android firmware that ships with most phones are spying on their users and custom ROMs are better as to ensure your phone doesn't tell the company you bought it from what you're doing however.
Apple users are very loud, but always remember, they are a minority.