‘posts_per_page’ => ’10’ does not show any post

after days of research, I found that the fault was simply in the pagination.
By changing the pagination code, I have made it work.

<?php

                $paged = (get_query_var('paged')) ? get_query_var('paged') : 1;

                $custom_args = array(
                    'post_type' => 'veranstaltungen',
                    'orderby' => 'date',
                    'order' => 'DESC',
                    'paged' => $paged,
                    'posts_per_page' => '10'
                );
                $wp_query = new WP_Query($custom_args);

                if ($wp_query->have_posts()) : while ($wp_query->have_posts()) : $wp_query->the_post();

                    ?>

                    <div class="accordion">
                        <div class="columns is-mobile is-flexend ">
                            <div class="column is-half">
                                <div class="columns is-mobile is-vcentered">
                                    <div class="column is-one-fifth">
                                        <i class="angle fa fa-angle-down fa-2x" aria-hidden="true"></i>
                                    </div>
                                    <div class="column is-four-fifths">
                                        <?php
                                        $categories = get_the_terms($custom_args->ID, 'veranstaltungen-category');
                                        $cats=""; // set empty string as  value

                                        foreach ($categories as $i => $category) {
                                            if ($i) echo ', ';
                                            echo '<span>' . $category->name . '</span>';
                                        }
                                        ?>

                                        <div class="title">
                                            <?php the_title(); ?>
                                        </div>
                                    </div>
                                </div>

                            </div>
                            <div class="column is-half">
                                <div class="postdate">
                                    <p><?php the_field('tag') ?></p>
                                    <p><?php the_field('datum') ?></p>

                                </div>
                            </div>
                        </div>
                    </div>
                    <div class="thepanel">
                        <div class="theimage">
                            <?php the_post_thumbnail(); ?>
                        </div>
                        <?php the_content(); ?>
                    </div>
                <?php endwhile; ?>
                    <div class="columns is-mobile">
                        <div class="column is-3 is-offset-9">
                            <div class="pagination">
                                <?php
                                $nav = get_the_posts_pagination(array(
                                    'mid_size' => 2,
                                    'prev_text' => 'Zurück',
                                    'next_text' => 'Vor',
                                    'screen_reader_text' => 'A'
                                ));
                                $nav = str_replace('<h2 class="screen-reader-text">A</h2>', '', $nav);
                                echo $nav;
                                ?>
                            </div>
                        </div>
                    </div>
                <?php endif;
                wp_reset_query();
                ?>

Ahora funciona perfectamente. Gracias a todos