Hi Achim,

This file contains the links for categories/y and sub title:

wp-content/themes/kalium/tpls/portfolio-loop-item-categories.php

and modify the code to look like this:

// What to show
$portfolio_loop_subtitles = $portfolio_args['subtitles'];

// Hide option is selected
if ( $portfolio_loop_subtitles == 'hide' ) {
	return;
}

// Show Subtitle
if ( $portfolio_item_subtitle ) {
	echo '<p class="sub-title">' . do_shortcode( $portfolio_item_subtitle ) . '</p>';	
}

// Categories
if ( ! empty( $portfolio_item_terms ) ) {
	$j = 0;
	
	echo '<p class="terms">';
	
	foreach ( $portfolio_item_terms as $term ) :
	
		// Term Separator
		echo $j > 0 ? ', ' : '';
	
		?><a href="<?php echo esc_url( kalium_portfolio_get_category_link( $term ) ); ?>" data-term="<?php echo esc_attr( $term->slug ); ?>">
			<?php echo esc_html( $term->name ); ?>
		</a><?php
	
		$j++;
	
	endforeach;
	
	echo '</p>';
}

This will work for you. 

Also don't forget to move this file in child theme because upcoming updates will replace it again if left in parent theme folder.