How can I get “Previous” and “Next” to show in the navigation besides the links?

You may like to use the_posts_pagination() instead of the_posts_navigation() or get_next/previous_posts_link().
The posts pagination function outputs a set of page numbers with links to the previous and next pages of posts.
Example format would be like this below:

<div class="pagination_style">
  <?php     
     the_posts_pagination(array (
                            'prev_text'     => __( 'PREV' ),
                            'next_text'     => __( 'NEXT' ),                                   
                            'screen_reader_text' => __( ' ' ),                                  
                         ));    
  ?>
</div>

.

Extra Lines about CSS: Implementing your own CSS styling you could handle the look and feel.
As an example, I coded which outputs like this –

You may see the CSS code as well.

.pagination_style{ margin: -5% 0 5%; text-align: center; }
.pagination_style a {color:black; text-align:center; padding: .5em 1em; text-decoration:none; transition:background-color .5s;-moz-transition:background-color .3s; -webkit-transition: background-color .3s; width: 50%;}
.pagination_style span.current {background-color: #4caf50; color: white; padding: .5em 1em; }
.pagination_style a:hover {background-color: #ccc;}

It can be noted that if you right-click on the page-number link to inspect you would see current class is auto-generated inside span as an active selector.

Hope this helps.