Create a new node when a field is added to a node How can a element (say an image) that is entered as a field (when creating a new node), also be created as a separate new node at the same time (either through copying the image or by referencing it)?
Option A

I myself wouldn't do that - I think that generally it's a practice that doesn't worth the time and risks (as would be explained in Option B) but anyway:

In drupal 7 this can be done with the Multi Node Add module. There isn't a version for Drupal 8 yet; If you don't have the knowledge to port it to Drupal 8 you might hire a PHP programmer to do that for you. An alternative would be to copy the desired fields from 1 node to another via this module. This module is going through a porting process at this era.

Guessing that both modules work only on 1 content type at a time, and can't recreate content in another Content type: You could handle that by cloning your nodes inside the same content type (X) with Node Clone or a similar module, and than convert all clones to their other, similar content type (Y) with Node Convert or a similar module.

Option B - Advice and workaround with Views.

As an SEOer, I would recommend on finding other way to enrich your sites' content; Cloned content is quite a good recipe for lowering both your PQS (Page quality scores) and in some cases - Your PageRanks as well... This becomes more serious with every passing year.

It could be better to create more sophisticated content pieces based on the first node content via the Views module (which is part of the Drupal 8 core); Here is an intro to Views 8. Many tutorials are available in Youtube for that module.