How to determine if an activity is opening for the first time?

You can check for saved state in onCreate: if null, the activity is created for the first time (without restoration after destruction). You can also use a flag in SharedPreferences or a static variable, but these are less reliable approaches for determining the first launch of the activity within the current process.

class MyActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_my)

        if (savedInstanceState == null) {
            // Activity is created for the first time
        } else {
            // Activity is restored from saved state
        }
    }
}

To determine the first launch of the application or a specific screen during the entire installation period, use SharedPreferences:

class MyActivity : AppCompatActivity() {

    private val PREFS_NAME = "MyPrefs"
    private val KEY_FIRST_LAUNCH = "firstLaunch"

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_my)

        val prefs = getSharedPreferences(PREFS_NAME, MODE_PRIVATE)
        val isFirstLaunch = prefs.getBoolean(KEY_FIRST_LAUNCH, true)

        if (isFirstLaunch) {
            // This is the first launch of the app or this screen
            // Perform first launch actions

            // Save flag that first launch has been done
            val editor = prefs.edit()
            editor.putBoolean(KEY_FIRST_LAUNCH, false)
            editor.apply()
        } else {
            // Not the first launch
        }
    }
}