Android app is installed on OS less than minSDKversion

I have an android app that is implemented using Flutter. In the app/build.gradle file minSDKversion is set to 23

 defaultConfig {
        applicationId "x"
        minSdkVersion 23
        targetSdkVersion 30
        versionCode 112
        versionName "0.01.12"
        multiDexEnabled true
    }

However, I'm getting some crash reports on Android 4.1.2.

java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.UnsatisfiedLinkError: Couldn't load flutter: findLibrary returned null

How the user has installed the app on less than minSDKversion? How is it possible and what can i do?