How to display specific title on Customizer?

You can create a Custom Control for WP Customizer and use it.
For example:

    class Sub_Section_Heading_Custom_Control extends WP_Customize_Control {

        //The type of control being rendered
        public $type="sub_section_heading";



        //Render the control in the customizer

        public function render_content() {

        ?>
            <div class="sub-section-heading-control">
                <?php if( !empty( $this->label ) ) { ?>
                    <h4 class="customize-control-title">
                          <?php echo esc_html( $this->label ); ?>
                    </h4>
                <?php } ?>

            </div>
        <?php
        }
    }

Add some CSS

.sub-section-heading-control 
    .customize-control-title{ 

   text-align: center;
   color: white;
   background-color: saddlebrown;
   padding: 10px;

    }

And add it to a section in Customizer:

$wp_customize->add_setting('heading_post_content', array()); // dummy

$wp_customize->add_control( new Sub_Section_Heading_Custom_Control( 
            $wp_customize, 'heading_post_content',
            array(
                'label'   => __( 'Post Content', 'your-text-domain' ), // Set heading text here
                'section' => 'post_single', // set section id here
            )
        ) );

It should look like this:

I hope this helps.