Tis tutorial provides the steps to change default excerpt to show custom post field. This tutorial uses the flexible content but can be work on any field.
In child-theme/functions.php, add
add_filter('the_excerpt', 'your_function_name'); function your_function_name($excerpt) { if( have_rows('flexible') ): while ( have_rows('flexible') ) : the_row(); if( get_row_layout() == 'flexible_name' ): $my_acf_field = wp_trim_words(get_sub_field('custom_excerpt'), 100); echo ''.$my_acf_field.''; endif; endwhile; else: endif; }
More: https://www.advancedcustomfields.com/resources/flexible-content/