Hello Muhammad,

My answers inline, bolded:

• I would like to ask that in showcase carousel where can I add the_content function to work with elementor??

Not recommended, as the carousel has been designed to run on its own without content. However, if you must, plz open portfolio-carousel-page.php and add the following line

<?php the_content(); ?>

on line 42 (before) or line 210 (after) the carousel

• How can I make multiple copy of that same carousel functionality on the same page??

You can't to put it shortly, as this is a page template. You do however have the content looped carousel and the content small looped carousel

http://clapat-themes.com/wordpress/serano/multimedia/

that you can add multiple instances in the same page. They are implemented as Gutenberg blocks or Elementor widgets

• I would like to use same style carousel without using portfolio hero image / video function. directly via gallery or random posts.

I'm not sure how is this possible. Perhaps you can use a plugin instead that does that (and make sure it's working with AJAX page transitions too)?

• carousel Items on click shows pop up light box style image instead of taking to another page.

See my answer to your prev question above

• items on carousel display different sizes but with desired aspect ratio

Perhaps this is a question I can forward to our webdesigner