If we have ACF flexible content rows setup on the page, display those. Otherwise, display the standard content.

acf-flexible-or-standard-content.php

<?php
// If have flexible content rows
if (have_rows('layouts')) :

  while (have_rows('layouts')) : the_row();

    $class = 'container';
    if (get_sub_field('background_color')) {
      $class .= ' ' . get_sub_field('background_color');
    }
    if (get_sub_field('background_pattern')) {
      $class .= ' ' . get_sub_field('background_pattern');
    }

?>

    <div class="<?php echo $class; ?>">

      <?php
      if (have_rows('content')) :

        // loop through the rows of data
        while (have_rows('content')) : the_row();

          get_template_part('template-parts/flex', get_row_layout());

        endwhile;

      else :
      ?>
      <?php // if no flexible content rows, display standard content ?>
        <div class="container">
          <div class="layout">
            <div class="column">
              <?php the_content(); ?>
            </div>
          </div>
        </div>
      <?php
      endif;
      ?>
    </div>
<?php
  endwhile;
endif;
?>