I want to display related portfolio post below single post portfolio. can you guys please help me.
This feature is not available out of the box and would require customization which goes beyond the scope of our support. However, we can provide you some ideas to get you started. You can start of by installing a child theme and do the customizations from there.
Basically, if you want to customize the single portfolio page, you can do the override for the file
content-portfolio.php which you can find in
wp-content/themes/pro/framework/views/ethos/. You can then search up for plugins that can extract the related post and use the shortcode to add it on the page.
Hope this gives you and idea how to get started.