How to Prevent Unwanted URL Indexing in nopCommerce for Better SEO?

I recently purchased two nopCommerce licenses for my new projects. However, I discovered that some pages on my site are being indexed by Google when they shouldn't be. For instance, the following URL is being indexed:

https://demo.nopcommerce.com/category/products?categoryId=2
or
https://demo.nopcommerce.com/category/products?categoryId=3&pagenumber=1

This URL is generated by nopCommerce, and similar URLs can be created by changing the category or page number IDs. This is detrimental to SEO, and Google has started indexing such URLs from my website.

The page should return 404.
How can I prevent these pages from being generated automatically? Can anyone help?

I don't think "The page should return 404", as they may be used (possibly by AJAX).
Rather, you can use Robots.txt.  (Google will respect it.)

In the administration panel, General Settings,  "Robots.txt" section, use the "Disallow paths" field to specify URLs that you want to disallow search engine crawlers from indexing.  E.g., add "/category/products"

Oh, I just noticed that /category/products/ is already there.  Check that.  
Put this in your browser for your site's URL

https://demo.nopcommerce.com/robots.txt

Do you see  /category/products/ ?

What version of nopCommerce?

I am using version 4.70. I can already see '/category/products/' in the robots.txt file. Let me change it to '/category/products?' and confirm within a week.