display_featured_image_on_fluent_form_from_post.php

add_filter('fluentform/rendering_field_data_custom_html', function ($data, $form)
{
   if($form->id != 50) { //change the form id with your own form id
      return $data;
   }
   
    global $post;

	  $thumbnail_id = get_post_meta( $post->ID, '_thumbnail_id', true ); // Get the thumbnail ID

	  if ( $thumbnail_id ) {
	
      $image_url = wp_get_attachment_image_url( $thumbnail_id, 'full' ); // Get the image URL

      $data['settings']['html_codes'] = '<img src="' . esc_url( $image_url ) . '" width=300, height=300 alt="" />'; // Display the image
	
	  }

   // Do your stuffs here
   return $data;
}, 10, 2);