if($i % 2 !=== 0)
<?php $portfolio_posts = new WP_Query( [
'post_type' => 'portfolio',
'posts_per_page' => - 1,
] ); ?>
<?php $increment = 1; ?>
<?php if ( $portfolio_posts->have_posts() ) : while( $portfolio_posts->have_posts() ) : $portfolio_posts->the_post(); ?>
<?php var_dump($increment); ?>
<?php if ( $increment % 2 !== 0 ): ?>
<div class="portfolio-item-wrap">
<?php endif ?>
<div class="portfolio-item">
<a class="overlay" href="<?php the_field( 'link_to_project' ); ?>" target="_blank">
<span class="portfolio-content">
<h1><?php the_title(); ?></h1>
<h4><?php the_content(); ?></h4>
</span>
</a>
<?php the_post_thumbnail( 'small' ); ?>
</div>
<?php if ( $increment % 2 === 0 ): ?>
</div>
<?php endif ?>
<?php ++$increment; ?>
<?php endwhile; ?>