OfflineNotice.js

import React, { PureComponent } from 'react';
import { View, Text, NetInfo, Dimensions, StyleSheet } from 'react-native';

const { width } = Dimensions.get('window');

function MiniOfflineSign() {
  return (
    <View style={styles.offlineContainer}>
      <Text style={styles.offlineText}>No Internet Connection</Text>
    </View>
  );
}

class OfflineNotice extends PureComponent {
  state = {
    isConnected: true
  };

  componentDidMount() {
    NetInfo.isConnected.addEventListener('connectionChange', this.handleConnectivityChange);
  }

  componentWillUnmount() {
    NetInfo.isConnected.removeEventListener('connectionChange', this.handleConnectivityChange);
  }

  handleConnectivityChange = isConnected => {
      this.setState({ isConnected });
  };

  render() {
    if (!this.state.isConnected) {
      return <MiniOfflineSign />;
    }
    return null;
  }
}

const styles = StyleSheet.create({
  offlineContainer: {
    backgroundColor: '#b52424',
    height: 30,
    justifyContent: 'center',
    alignItems: 'center',
    flexDirection: 'row',
    width,
    position: 'absolute',
    top: 30
  },
  offlineText: { color: '#fff' }
});

export default OfflineNotice;

I've updated componentDidMount to read the initial connection state, so the message is displayed when the app launches if the user is offline:

  componentDidMount () {
    NetInfo.isConnected.fetch().then(this.handleConnectivityChange)

    NetInfo.isConnected.addEventListener('connectionChange', this.handleConnectivityChange)
  }

also, if the screen rotates, width doesn't get updated... there's a workaround by setting:

const styles = StyleSheet.create({
  offlineContainer: {
    // don't set width
    left: 0,
    right: 0
    // ...
  },
//...

another smaller comment is that both if/else cases in handleConnectivityChange do the same - could be replaced with:

  handleConnectivityChange = isConnected => {
    this.setState({ isConnected })
  }

Tried to make this work in Expo App with typescript.
Think it works now (2022-11).Got a fork.