Add Jetpack Markdown support for ACF

render.php

<?php
// Add these filters in functions.php
add_filter( 'meta_content', 'wptexturize'        );
add_filter( 'meta_content', 'convert_smilies'    );
add_filter( 'meta_content', 'convert_chars'      );
add_filter( 'meta_content', 'wpautop'            );
add_filter( 'meta_content', 'shortcode_unautop'  );
add_filter( 'meta_content', 'prepend_attachment' );


// The rendering part
function render_acf() {
  
  if( have_rows('flexible_content_field_name') ):
  
    while ( have_rows('flexible_content_field_name') ) : the_row();
  
      if( get_row_layout() == 'content' ):

        $content = get_sub_field( 'content' );
        // You might want to check whether WPCom_Markdown exists
        $content = WPCom_Markdown::get_instance()->transform( $content , array( 'id' => false, 'unslash' => false ) );
        $content = apply_filters( 'meta_content', $content );
        echo $content;

      endif;

    endwhile;

  else :
    // no layouts found
  endif;
  
}