I mean just products from external websites. So instead of clicking on the button "Add to Cart" it should be for example “Buy on Amazon" or something like that.
And I would like to store them in my own database. So to import the products with a CSV file into my shop.
... if NopCommerce can handle the amount of over 1 million affiliate products
Probably, but it really depends on the performance of your servers, including database server, and whether you require Specification Attributes to be searched. (will you have a Faceted Search navigation?)
You may want to look at / test the stored procedure PROCEDURE [dbo].[ProductLoadAllPaged]
(although I believe that 3rd party faceted search plugins may have their own stored procedures).