A simple sample to query two Custom Post Types with a tax_query

query.php

<?php 

$args = [
'post_type' => ['post', 'work'],
'posts_per_page' => -1,
'tax_query' => [
  'relation' => 'OR',
  [
    'taxonomy' => 'post_tag',
    'field' => 'slug',
    'terms' => 'tag-two'
  ],
  [
    'taxonomy' => 'category',
    'operator' => 'NOT EXISTS'
  ]
]
];

$posts = new WP_Query($args);