What is wrong on this below code?

The ads are appearing when I change the screen but before loading the Ads I am getting white screen for 2-3 seconds.

Why it's happening? Thank you in advance for your time and support.

import React, { useState, useEffect } from "react"; import { View, Button, Text, ScrollView, } from 'react-native' import { RewardedAd, RewardedAdEventType, TestIds } from 'react-native-google-mobile-ads'; const adUnitId = __DEV__ ? TestIds.REWARDED : 'ca-app-pub-3940256099942544/5224354917';     const rewarded = RewardedAd.createForAdRequest(adUnitId, {       requestNonPersonalizedAdsOnly: true,       keywords: ['fashion', 'clothing'],     });     const Testing = ({ navigation }) =>{             const [loaded, setLoaded] = useState(false);         useEffect(() => {               const unsubscribeLoaded = rewarded.addAdEventListener(RewardedAdEventType.LOADED, () => {                 setLoaded(true);                 rewarded.show();               });               const unsubscribeEarned = rewarded.addAdEventListener(                 RewardedAdEventType.EARNED_REWARD,                 reward => {                   console.log('User earned reward of ', reward);                 },               );           // Start loading the rewarded ad straight away               rewarded.load();           // Unsubscribe from events on unmount               return () => {                 unsubscribeLoaded();                 unsubscribeEarned();               };             }, []);                        // No advert ready to show yet             if (!loaded) {               return null;             }             return (                 <ScrollView>                 <View style={{flex:1, justifyContent : 'center',alignItems : 'center'}}>                 <Text>                  Lorem Ipsum is simply dummy text of the printing and typesetting industry.                 Lorem Ipsum has been the industry's standard dummy text ever since the 1500s,                  </Text>                 <Button onPress = {() => navigation.navigate('ThirdPage')} title='Next Screen'></Button>                    </View>                 </ScrollView>)             }             export default Testing