If you have the image string, you need to use an image processing library for displaying your images in an image view. Some of the popular libraries are Coil, Glide and Picasso.
A simple way to display your image, if you are using let’s say Glide, would be

Glide.with(context).load(imgCar).into(itemView.imgCar)

class AdapterPostagem ( val car: MutableList): RecyclerView.Adapter<AdapterPostagem.CarViewHolder>(){

inner class CarViewHolder ( itemView: View ): RecyclerView.ViewHolder( itemView ) {
    fun bind(car: Car) {
        with(car) {
            itemView.txtNameCar.text = nameCar
            itemView.txtBrandCar.text = brandCar
            //This line, in AndroidStudio not accept this formated
            itemView.imgCar.imageView = imgCar
            itemView.txtDescri.text = descCar
            itemView.txtPrice.text = priceCar
            itemView.txtYearsCar.text = yearCar
        }
    }

}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CarViewHolder {
    val view =  LayoutInflater.from(parent.context).inflate(R.layout.adapter_postagem, parent, false)
    return CarViewHolder( view )
}

override fun getItemCount(): Int = car.size

override fun onBindViewHolder(holder: CarViewHolder, position: Int) {
    holder.bind( car[position])
}

}