Before choosing the minimum OS version for a mobile app, check how many of your users are on each release. Google publishes Android version distribution in Android Studio and the Play Console shows your own audience, while Apple’s App Store analytics give the same for iOS.
As a rule of thumb, setting minSdk (Android) and the deployment target (iOS) so that roughly 95 percent of your audience is covered balances reach against maintenance cost. Dropping very old versions lets you use modern APIs, security features and Material 3 or SwiftUI.
Updated for today: instead of counting versions by hand, rely on Jetpack libraries and AndroidX compatibility layers, test on real devices in a cloud device lab, and review your numbers every release cycle.