Thank you, Greg. It helps!
I achieved the display of a custom field on ads list by adding the code given here in my theme functions.php file and by adding the following code in the list-item.php file:
<?php $customfield = get_post_meta( get_the_ID(), "my_custom_checkbox", true ) ?>
<?php if( $customfield ): ?>
<div ><?php esc_html_e(( get_post_meta( get_the_ID(), "my_custom_checkbox", true ) ) ) ?></div>
<?php endif; ?>
But I dont know how to do the same thing with a checkbox custom-field. Can you help me again, please?
Guylaine