在您的代码中，您已经在堆栈组件中创建了Login组件，并在堆栈组件中声明了电子邮件和密码状态，因此当您更改电子邮件或密码状态时，堆栈组件将重新呈现，并与该Login组件沿着卸载（或完全销毁）并再次装载。这就是键盘消失的原因。因此，为了使代码正常工作，您可以将登录组件移出堆栈组件，并将密码和电子邮件状态以及所有导航处理程序移入登录组件。
更正后的代码如下所示。

import { createStackNavigator } from "@react-navigation/stack";
import React, { useState } from "react";
import {
  View,
  Text,
  TextInput,
  TouchableOpacity,
  Image,
  StyleSheet,
} from "react-native";
import { NavigationContainer } from "@react-navigation/native";
// Screens
import MainContainerScreen from "./MainContainerScreen";
import RegisterScreen from "./RegisterScreen";
import ForgotPasswordScreen from "./ForgotPasswordScreen";
// Screen Names
const MainContainerName = "Main";
const registerName = "Inscription";
const forgotPasswordName = "Mot de passe oublié";
const Stack = createStackNavigator();
function Login({ navigation }) {
  const [email, setEmail] = useState("");
  const [password, setPassword] = useState("");
  const handleLogin = (navigation) => {
    // Redirection vers l'interface MainContainer (TabNavigator)
    navigation.navigate(MainContainerName);
  };
  const handleForgotPassword = (navigation) => {
    // Redirection vers la page de réinitialisation du mot de passe
    navigation.navigate(forgotPasswordName);
  };
  const handleFirstTimeLogin = (navigation) => {
    // Redirection vers un autre écran pour la première connexion
    navigation.navigate(registerName);
  };
  return (
    <View style={styles.container}>
      <Image source={require('../../assets/icon.png')} style={styles.logo} />
      <TextInput
        placeholder="Adresse e-mail"
        value={email}
        onChangeText={setEmail}
        style={styles.input}
      />
      <TextInput
        placeholder="Mot de passe"
        value={password}
        onChangeText={setPassword}
        secureTextEntry
        style={styles.input}
      />
      <TouchableOpacity
        onPress={() => handleLogin(navigation)}
        style={styles.button}
      >
        <Text style={styles.buttonText}>Connexion</Text>
      </TouchableOpacity>
      <TouchableOpacity onPress={() => handleForgotPassword(navigation)}>
        <Text style={styles.forgotPasswordText}>Mot de passe oublié</Text>
      </TouchableOpacity>
      <TouchableOpacity onPress={() => handleFirstTimeLogin(navigation)}>
        <Text style={styles.firstTimeLoginText}>Première connexion</Text>
      </TouchableOpacity>
    </View>
  );
}
export default function LoginPage() {
  return (
    <NavigationContainer>
      <Stack.Navigator>
        <Stack.Screen
          name="Login"
          component={Login}
          options={{ headerShown: false }}
        />
        <Stack.Screen
          name={forgotPasswordName}
          component={ForgotPasswordScreen}
          options={{ headerShown: false }}
        />
        <Stack.Screen
          name={registerName}
          component={RegisterScreen}
          options={{ headerShown: false }}
        />
        <Stack.Screen
          name={MainContainerName}
          component={MainContainerScreen}
          options={{ headerShown: false }}
        />
      </Stack.Navigator>
    </NavigationContainer>
  );
}
const styles = StyleSheet.create({
  container: {
    flex: 1,
    alignItems: "center",
    justifyContent: "center",
  },
  logo: {
    width: 150,
    height: 150,
    marginBottom: 50,
  },
  input: {
    width: "80%",
    height: 40,
    borderWidth: 1,
    borderColor: "gray",
    borderRadius: 5,
    marginBottom: 10,
    paddingHorizontal: 10,
  },
  button: {
    backgroundColor: "blue",
    width: "80%",
    height: 40,
    alignItems: "center",
    justifyContent: "center",
    borderRadius: 5,
    marginBottom: 10,
  },
  buttonText: {
    color: "white",
    fontSize: 16,
  },
  forgotPasswordText: {
    color: "blue",
    marginBottom: 10,
  },
  firstTimeLoginText: {
    color: "blue",
  },
});