I’m trying to list posts from a CPT named “exposition” and group them based on a custom taxonomy called “date-exposition” (which are meant to be years such as 2010, 2015, 2017,…) in the following form :

2019

2018

etc…

Closest code I managed to compile is this (it only shows one date/taxonomy-value and not the posts…) :

<?php
    // Get current Category
    $get_current_cat = get_term_by('name', single_cat_title('',false), 'category');
    $current_cat = $get_current_cat->term_id;


    // List posts by the terms for a custom taxonomy of any post type
    $post_type="exposition";
    $tax = 'date-exposition';
    $tax_terms = get_terms( $tax, 'orderby=name&order=ASC');
    if ($tax_terms) {
        foreach ($tax_terms  as $tax_term) {
            $args = array(
                'post_type'         => $post_type,
                "$tax"              => $tax_term->slug,
                'post_status'       => 'publish',
                'posts_per_page'    => -1,
                'category__in'      => $current_cat // Only posts in current category (category.php)
            );

            $my_query = null;
            $my_query = new WP_Query($args);

            if( $my_query->have_posts() ) : ?>

                <h2><?php echo $tax_term->name; // Group name (taxonomy) ?></h2>

                <?php while ( $my_query->have_posts() ) : $my_query->the_post(); ?>
                    <?php $term_list = wp_get_post_terms($post->ID, 'category', array("fields" => "ids")); // Get post categories IDs?>

                    <?php if (in_array($current_cat, $term_list) ): // Display only posts that have current category ID ?>
                        <h3><?php the_title(); ?></h3>
                    <?php endif; // if in_array ?>

                <?php endwhile; // end of loop ?>

            <?php endif; // if have_posts()
            wp_reset_query();

        } // end foreach #tax_terms
    } // end if tax_terms
?>

Thanks for help. Please note I am really not good at PHP.