I am doing bottom navigationview but my Fragments are stacking on top of each other

Question

I am new in android and I don't know what's up with my code I need help I put 2 or 3 code in same one and somehow works, but only problem I have with this is In Android Studio, I started a new project with bottomNavigationView and now when I run the application in the emulator, the Home Fragment is there by default but then is never replaced when I switch to another fragment. Instead, the new fragments replace each other while still being on top of the first fragment. So if I had 3 fragments, fragment 1 stays stuck in the activity while fragment 1 (duplicate), fragment 2, and fragment 3 all replace each other on top of fragment 1 (original). I don't know how to get rid of the original fragment, or where it is even coming from. I'm new to Android development and learning so I am struggling to find suggestions. Here is the code in my mainactivity:

import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.MenuItem;
import android.view.View;
import android.view.Menu;
import android.widget.ImageView;
import android.widget.Toast;

import com.abc.finalprojectscreen.ui.gallery.GalleryFragment;
import com.abc.finalprojectscreen.ui.home.HomeFragment;
import com.abc.finalprojectscreen.ui.slideshow.SlideshowFragment;
import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.google.android.material.internal.NavigationMenuView;
import com.google.android.material.snackbar.Snackbar;
import com.google.android.material.navigation.NavigationView;

import androidx.annotation.NonNull;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.widget.Toolbar;
import androidx.core.view.GravityCompat;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.appcompat.app.AppCompatActivity;

import com.abc.finalprojectscreen.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener , BottomNavigationView.OnItemSelectedListener {

    private AppBarConfiguration mAppBarConfiguration;

    NavigationView navigationView;
    BottomNavigationView navigation;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        navigation = findViewById(R.id.navigation);
        navigation.setOnItemSelectedListener(this);




        navigationView = (NavigationView) findViewById(R.id.nav_view);
        loadFragment(new home1());
        navigationView.setNavigationItemSelectedListener(this);


        Fragment fragment = new HomeFragment();
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.nav_host_fragment_content_main, fragment);
        fragmentTransaction.commit();
    }

    private boolean loadFragment(Fragment fragment) {
        //switching fragment
        if (fragment != null) {
            getSupportFragmentManager()
                    .beginTransaction()
                    .replace(R.id.fragmentLayout, fragment)
                    .commit();
            return true;
        }
        return false;
    }



//   @Override
//    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
//        Fragment fragment = null;
//
//        switch (item.getItemId()) {
//            case R.id.home:
//                fragment = new home1();
//                break;
//
//            case R.id.video:
//                fragment = new video();
//                break;
//
//            case R.id.help:
//                Intent i =new Intent(MainActivity.this,helpa.class);
//                startActivity(i);
//                break;
//            case  R.id.Menu:
//                DrawerLayout drawer = (DrawerLayout)findViewById(R.id.drawer_layout);
//                drawer.openDrawer(GravityCompat.START);
//                return true;
//        }
//
//        return loadFragment(fragment);
//
//    }


    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        Fragment fragment = null;
        String title = getString(R.string.app_name);
        int id = item.getItemId();
        switch (item.getItemId()) {
            case R.id.home:
                fragment = new home1();
                loadFragment(fragment);
                break;

            case R.id.video:
                fragment = new video();
                loadFragment(fragment);
                break;

            case R.id.help:
                Intent i =new Intent(MainActivity.this,helpa.class);

                startActivity(i);
                break;
            case  R.id.Menu:
                DrawerLayout drawer = (DrawerLayout)findViewById(R.id.drawer_layout);
                drawer.openDrawer(GravityCompat.START);
                return true;
        }


        if (id == R.id.nav_home) {
            fragment = new HomeFragment();
            title = "Home";
        } else if (id == R.id.help_app) {
            Intent i =new Intent(MainActivity.this,helpa.class);
            startActivity(i);
        } else if (id == R.id.more_apps) {
            fragment = new SlideshowFragment();
            title = "Feedback";

        } else if (id == R.id.rate_app) {
            Uri uri = Uri.parse("https://play.google.com/store/apps/details?id=" + getApplicationContext().getPackageName());
            Intent i = new Intent(Intent.ACTION_VIEW, uri);
            try {
                startActivity(i);
            } catch (Exception e) {
                Toast.makeText(this, "Unable to open\n" + e.getMessage(), Toast.LENGTH_SHORT).show();
            }
        } else if (id == R.id.share_app) {
            try {
                Intent i = new Intent(Intent.ACTION_SEND);
                i.setType("text/plain");
                i.putExtra(Intent.EXTRA_SUBJECT, "Wisdom locator");
                i.putExtra(Intent.EXTRA_TEXT, "https://play.google.com/store/apps/details?id=" + getApplicationContext().getPackageName());
                startActivity(Intent.createChooser(i, "Share With"));
            } catch (Exception e) {
                Toast.makeText(this, "Unable to open\n" + e.getMessage(), Toast.LENGTH_SHORT).show();
            }
        }
            DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
            drawer.closeDrawer(GravityCompat.START);
            if (fragment != null) {
                FragmentManager fragmentManager = getSupportFragmentManager();
                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                fragmentTransaction.replace(R.id.fragmentLayout, fragment);
                fragmentTransaction.commit();
                setTitle(title);
            }
            return true;
        }


    }

thank for your Ans so mix both of them in same one so it is little confusing