The easy-but-a-bit-hacky way to get there would be to initialize a counter variable before your loop and then use that to tell what post you’re on. something like so:
$paged = (get_query_var('paged')) ? absint(get_query_var('paged')) : 1;
$args = array(
'post_type' => 'workshop',
'post_status' => 'publish',
'posts_per_page' => 11,
'paged' => $paged,
);
$customQuery = new WP_Query($args);
$counter = 1;
if ($customQuery->have_posts()) :
while ($customQuery->have_posts()) : $customQuery->the_post();
if ($counter === 1) { ?>
<div class="row">
<!-- ROW 1 - FULL SCREEN WIDTH MARKUP -->
</div><!--/.row-->
<?php
} elseif ($counter <= 5) {
if ($counter === 2) { ?>
<div class="row no-gutters">
<?php }
?>
<!-- ROW 2 - [FOUR POSTS] MARKUP HERE -->
<?php if ($counter === 5) { ?>
</div><!--/.row-->
<?php }
} else {
if ($counter === 6) { ?>
<div class="row no-gutters">
<?php } ?>
<!-- ROW 3 - [Six Posts] Markup -->
<?php if ($counter === 11) { ?>
</div><!--/.row-->
<?php }
};
$counter++;
endwhile;
endif;