You could wrap it in an if
statement to check if $projects
is empty.
<?php
$projects = get_field('projects');
if ( $projects ) :
?>
<h2>Supported projects</h2>
<hr class=”bg__yellow”>
<div class="posts">
<?php foreach( $projects as $post) : setup_postdata($post); ?>
// Your code here...
<?php endforeach; wp_reset_postdata(); ?>
</div>
<?php endif; ?>