根据Laravel文档，如果中间表有额外的列，则需要在定义关系时指定

//Product
public function attributeProduct(){
    return $this->belongsToMany(
        AttributeProduct::class,
        'attribute_product_values',
        'product_id',
        'attribute_id'
    )
    ->withPivot('value');
    //If you want created_at and updated_at on pivot table
    ///withTimestamps();
}


//AttributesProduct

public function product()
{
    return $this->belongsToMany(
        Product::Class,
        'attribute_product_values',
        'attribute_id',
        'product_id'
    )
    ->withPivot('value');
    //If you want created_at and updated_at on pivot table
    ///withTimestamps();
}

访问中间表中的列

$attributeProduct = AttributesProduct::find(1);

foreach($arrtibutesProduct->products as $prouct)
{
    $product->pivot->value;
}

你可以自定义pivot属性名称

参见https://laravel.com/docs/8.x/eloquent-relationships#retrieving-intermediate-table-columns