Как выделить текст построчно в React Native

Вы можете использовать для этого библиотеку реагировать родной-выделить-слова.

Вот пример:

import React, { Component } from 'react';
import { Text, View } from 'react-native';
import Highlighter from 'react-native-highlight-words';

export default class Example extends Component {
  render() {
    return (
      <View style = {{alignItems: 'center', paddingTop: 300}}>
        <Highlighter
          highlightStyle = {{backgroundColor: 'greenyellow'}}
          searchWords = {["Swine Flu is an infection caused by"]}
          textToHighlight = "Swine Flu is an infection caused by..."
        />
        <Highlighter
          highlightStyle = {{backgroundColor: 'lightblue'}}
          searchWords = {["swine flu"]}
          textToHighlight = "The risk of swine flu..."
        />
      </View>
    );
  }
}