The returned data from https://reqres.in/api/users?page=2 is not an array, but an object with a data property containing what you are looking for (an array). The result of the request is :

{"page":1,"per_page":6,"total":12,"total_pages":2,"data":[{"id":1,"email":"george.bluth@reqres.in","first_name":"George","last_name":"Bluth","avatar":"https://reqres.in/img/faces/1-image.jpg"},{"id":2,"email":"janet.weaver@reqres.in","first_name":"Janet","last_name":"Weaver","avatar":"https://reqres.in/img/faces/2-image.jpg"},{"id":3,"email":"emma.wong@reqres.in","first_name":"Emma","last_name":"Wong","avatar":"https://reqres.in/img/faces/3-image.jpg"},{"id":4,"email":"eve.holt@reqres.in","first_name":"Eve","last_name":"Holt","avatar":"https://reqres.in/img/faces/4-image.jpg"},{"id":5,"email":"charles.morris@reqres.in","first_name":"Charles","last_name":"Morris","avatar":"https://reqres.in/img/faces/5-image.jpg"},{"id":6,"email":"tracey.ramos@reqres.in","first_name":"Tracey","last_name":"Ramos","avatar":"https://reqres.in/img/faces/6-image.jpg"}],"support":{"url":"https://reqres.in/#support-heading","text":"To keep ReqRes free, contributions towards server costs are appreciated!"}}

So you cannot use map function, which is from the Array prototype, on the result of your request. You must access the data property first :

this.state.data.data.map((data, index) => ( // note the double data
  <li key={index}>Email: {data.email}</li>
))

You could also assign json.data to the state.data to avoid the ugly .data.data :

this.setState({
  isLoaded: true,
  data: json.data, // note the .data
});

I don't see any error, it's working just fine.

Output:

Working Example: StackBlitz

import * as React from 'react';
import { Text, View, StyleSheet } from 'react-native';
import Constants from 'expo-constants';
class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      data: [],
      isLoaded: false,
    };
  }

  componentDidMount() {
    fetch('https://reqres.in/api/users?page=2')
      .then((res) => res.json())
      .then((json) => {
        console.log(json.data);
        this.setState({
          isLoaded: true,
          data: json.data,
          email: null,
        });
      });
  }

  render() {
    var { isLoaded, data } = this.state;

    if (!isLoaded) {
      return <div>Is isLoaded</div>;
    } else {
      return (
        <div>
          <div className="contents home">
            <img
              src="https://trucard.io/india/wp-content/uploads/2021/08/2021-June-TruCard-Logo.png
"
              width={50}
              alt="img"
              className="trucard-img"
            />
          </div>
          <div className="button">
            <button className="button-button">Load list</button>
          </div>
          <ul>
            {this.state.data?.map((data, index) => (
              <li key={index}>Email: {data.email}</li>
            ))}
            ;
          </ul>
        </div>
      );
    }
  }
}

export default App;

I think the problem is in brackets around your .map() method. Please try this

class Home extends Component {
  constructor(props) {
    super(props);
    this.state = {
      data: [],
      isLoaded: false,
    };
  }

  componentDidMount() {
    fetch("https://reqres.in/api/users?page=2")
      .then(res => res.json())
      .then(json => {
        this.setState({
          isLoaded: true,
          data: json,
        });
      });
  }

  render() {
    const { isLoaded, data } = this.state;

    if (!isLoaded) {
      return <div>Is isLoaded</div>;
    } else {
      return (
        <div>
          <ul>
            {data?.map((data, index) => {
              return <li key={index}>Email: {data.email}</li>;
            })}
          </ul>
        </div>
      );
    }
  }
}

export default Home;