Target second from last post in loop

Question

You can achieve this by modifying your above shared code as following.

$prelimartPosts = new WP_Query($args2);

 while ($prelimartPosts->have_posts() ) : $prelimartPosts->the_post();

    if (($prelimartPosts->current_post +2) >= ($prelimartPosts->post_count)) {
       // This is last post and second last post
       get_template_part( 'template-parts/content', 'front-center' );

    } else {
       // These are all other posts except last and second last posts
       get_template_part('template-parts/content', 'front-bottom');

   }

endwhile;

If you want to use seperate conditions for each then use the below code instead of above.

$prelimartPosts = new WP_Query($args2);

 while ($prelimartPosts->have_posts() ) : $prelimartPosts->the_post();

    if (($prelimartPosts->current_post +1) == ($prelimartPosts->post_count)) {
        // This is last post
       get_template_part( 'template-parts/content', 'front-center' );

    } else if (($prelimartPosts->current_post +2) == ($prelimartPosts->post_count)) {
        // This is second last post
       get_template_part( 'template-parts/content', 'front-center' );

   } else {
        // These are all other posts except last and second last posts
       get_template_part('template-parts/content', 'front-bottom');

   }

endwhile;