Show only 12 post for each categories – portfolio

Goodmorning,
I want to show only 12 post for each categories in my portfolio page.
I’ve read some solutions but I’m very confused.
if anyone can help me I would be very grateful
This is my code:
…

<?php
			$portfolio_args = array(
				'post_type' => 'project',
				//'posts_per_page' => 12,
				'showposts' => (int) et_get_option('flexible_homepage_numposts_projects'),
				'tax_query' => array(
					array(
						'taxonomy' => 'project_category',
						'field' => 'id',
						'terms' => (array) et_get_option('flexible_homepage_exlcats_projects'),
						'operator' => 'NOT IN'
					)
				)
			);

			$categories = get_terms( 'project_category', array( 'exclude' => (array) et_get_option('flexible_homepage_exlcats_projects') ) );

			if ( $categories ){
				echo '<ul id="et_portfolio_sort_links">';
					//echo '<li class="active">' . '<a href="#">' . __( 'All', 'Flexible' ) . '</a>' . '';
					foreach ( $categories as $category ){
						echo '
<li>' . '<a href="#">term_taxonomy_id ) . '">' . esc_html( $category->name ) . '</a>' . '</li>
';
					}
				echo '';
			}
		?>

		<div id="portfolio-grid" class="clearfix">
		<?php
			$portfolio_query = new WP_Query( apply_filters( 'et_home_portfolio_args', $portfolio_args ) );
			while ( $portfolio_query->have_posts() ) : $portfolio_query->the_post();
				get_template_part( 'includes/entry', 'portfolio' );
			endwhile;
			wp_reset_postdata();
		?>
		</div> <!-- end #portfolio-grid -->
	</section> <!-- end #portfolio -->
<?php } ?>
...

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Thank you!