how to instanciate a relationship many-to-many ,and update it's columns

Question

i have a many-to-many relationship between Product and User models,I'm trying to instanciate one relationship between a user and a specific product Or updateit's column 'favoris' if it's already existing.

I'm not sure if im using the adequate methodes .

<?php

namespace App\Http\Controllers;

use App\Http\Middleware\Authenticate;
use App\Models\Product;
use Exception;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Auth;
use Illuminate\Support\Facades\Log;

class StatisticsController extends Controller
{
    public function favoris(Request $request){
       $user=Auth::user();
       $list_prods_fav_true=[];
        $favs=$request->input('favoris');
        Log::info($favs);
        $list_favoris=collect();
        $list_unfavoris=collect();
          $message='';
          try{
        foreach ($favs as $fav) {
          $prod= $fav['produit'];
        
          try{
            $product=Product::find($prod["id"]);
              if(!$product){
                       $product=Product::create(
                        [
                            'id'=>$prod["id"],
                            'nom'=>$prod["nom"],
                            'description'=>$prod["description"],
                            'img'=>$prod["img"]
                        ]
                        );}
                $nbre_lignes_updated=$user->products()->updateExistingPivot(
                $prod->id,['favoris'=>true]
                           );
                           if($nbre_lignes_updated===0){
                            Log::info('update '.$nbre_lignes_updated);
                            $user->products()->syncWithoutDetaching([$prod->id=>['favoris'=>true]]);
                           }                      
                array_push($list_prods_fav_true,$prod['id']);
                          
                        
                       
                       
                       


            
                }
                catch(Exception $e){
                    $message=$e;
                }
            
                  
            
/* 
            $product->updateExistingPivot($prod['id'],['favoris'=>true]);
            */
            $list_prods_fav_false=$user->products->diff(Product::whereIn('id',$list_prods_fav_true)->get());
           
            foreach($list_prods_fav_false as $prod){
               $nbre_lignes_updated=$user->products()->updateExistingPivot(
                $prod->id,['favoris'=>false]
               );
               if($nbre_lignes_updated===0){
                Log::info('upadte '.$nbre_lignes_updated);
                $user->products()->syncWithoutDetaching([$prod->id=>['favoris'=>false]]);
               }
               else{
                Log::info('update',$nbre_lignes_updated);
               }
            }
            $list_favoris=$user->products()->wherePivot('favoris',true)->get();
            $list_unfavoris=$user->products()->wherePivot('favoris',false)->get();
        
      
        }}
        catch(Exception $e){
            $message=$e;;
        }
       
        return response()->json([
            'message'=>'liste des favoris est bien recue  '. $message,
            'liste des favoris'=>$list_favoris,
            'liste des unfavoris'=>$list_unfavoris,
        ]);
    }
}

the result is always an empty array for list_favoris ,that's when i added updateExistingPivot, before i used only syncWithoutDetaching and it creates up to 4 relashionship objects every time i add one product to favorite.