Taxonomie cpt with acf

You would want to use the value of the ACF Taxonomy Field as an additional argument of your WP_Query. So in ‘single-formation.php’ replace your WP_Query with something like this:

$term_ids = get_field('taxonomy_field_name'); // make sure the return value of your ACF Taxonomy field is set to "Term ID"

$args = array(
    'post_type' => 'formation',
    'tax_query' => array(
        array(
            'taxonomy' => 'thematique',
            'field'    => 'term_id',
            'terms'    => $term_ids,
        ),
    ),
);
$loop = new WP_Query( $args );

$loop should now contain any CPT ‘formations’ with the selected terms of the ‘thematique’ taxonomy.