SQL request with WP_Query, join OR between post_type and taxonomy

Hi.

My issue is pretty simple, I’m trying to get both portfolio posts (plugin) and articles that have the “portfolio” category (made myself).

$args = array(
        'post_type' => 'portfolio',
        'tax_query' => array(
            array(
                'taxonomy' => 'category',
                'field'    => 'slug',
                'terms'    => 'portfolio',
            )
        )
    );

    $query = new WP_Query($args);

It looks like the relationship between post_type and tax_query is an AND, I’d need an OR, how can I do that?

I tried following the official documentation but I’m stuck. (https://codex.ww.wp.xz.cn/Class_Reference/WP_Query)
Thanks for the help.