How to Create Columns with WordPress and CPTUI display page ?

Maybe this help you:

$ourposts = new WP_Query( $args );
// ask if there results
if( $ourposts->have_posts() ):
    $i = 0;
    // outside the while you open and close the tr so inside the while yo only have to print a close tr and reopen it
    echo '<tr>';
    while($ourposts->have_posts()) : $ourposts->the_post();
        $i++;
        // every three posts you closes and open a tr
        if( $i%3==0 ){
            echo '</tr><tr>';
        }
        echo '<td>'.get_the_title().'</td>';
    endwhile;
    // then close the tr
    echo '</tr>';
endif;