Try using the below in your newfeed.php. I was able to test using query_post by passing an array of the category details it had. I’ve also noticed we have to reset the query since it will be used to grab the page news in its own have_post() / the_post() if not it will overwrite the first the_content() loop.
<?php
defined( 'ABSPATH' ) || die( "Can't access directly" );
$args = array(
'category_name' => 'covid-updates',
'posts_per_page' => -1, // Get all
// Catagory ID can be used instead of slug
// 'cat' => 5,
'order' => 'ASC'
);
query_posts( $args );
if (have_posts()) : while (have_posts()) : the_post();
?>
<h1><?php the_title();?></h1>
<p><?php the_content();?></p>
<?php
endwhile;
endif;
wp_reset_query(); // Destroys the previous query and sets up a new query.
?>