Within a node template how can I tell what regions are in use/ occupied?

I am trying to create a preprocess function in my .theme file in order to make a variable available to node templates.

I want the variable to contain just the names of all regions that are currently in use (i.e. rendering content).

The idea being, if I have a region called left_hand_nav which is rendered on some (not all) pages, and I have a node called generic_page, from my generic_page node template I'd like to be able to do:

{% if left_hand_nav %}
 do something
{% else %}
 do something else
{% endif %}

I am not interested in controlling the rendering of any regions blocks from the node template. Instead for any given page wherein the node is rendered I just want to know if a particular region on said page is in use.

I realize this can very easily be done from a page template but instead of having a kazillion billion conditionals in my page template I'd prefer a few conditionals in several node templates.

If someone could point me in the right direction I'd appreciate it very much.

In special case of navigating to a node page (like when viewing an article) you can see that when implementing hook_preprocess_page , the $variables does contain a 'node' value, if you add any property to your $variables['node'] , you will be able to use it in node.html.twig file

Update

As in hook_preprocess_page you can access all regions using $variables['REGION_NAME'] , so that you can check them if they are empty or having content , if they weren't empty you can save their name in an array and then apply that array to $variables['node']