How do I render the page to add products into my custom module?
You need to create an empty product and use entity.form_builder service to generate the form.
Try the following.

&lt;?php

namespace Drupal\mymodule\Controller;

use Drupal\commerce_product\Entity\Product;
use Drupal\Core\Controller\ControllerBase;

class HelloController extends ControllerBase {
  public function content() {
   $product = Product::create([
     'type' =&gt; 'default',
   ]);
  return  \Drupal::service('entity.form_builder')-&gt;getForm($product);
  }
}