Show one post from certain category

I have created a template based on single.php in TwentyEleven, using the following code to show the latest post from category 5:

<?php // Display blog posts on any page
		$temp = $wp_query; $wp_query= null;
		$wp_query = new WP_Query(); $wp_query->query('showposts=1&cat=5');
		while ($wp_query->have_posts()) : $wp_query->the_post(); ?>
					<?php get_template_part( 'content', 'single' ); ?>

Works great!

I tried to transplant that code into a new template based on singular.php in TwentyTwenty and it does not work – I get an error of ‘unexpected end of page’. I have checked repeatedly for missing } ; and ?> but everything is in its place.

When adding the code, I removed

	<?php

	if ( have_posts() ) {

		while ( have_posts() ) {
			the_post();

			get_template_part( 'template-parts/content', get_post_type() );
		}
	}

	?>

But if I re-add the ‘if’ statement and the corresponding braces, I get an error of ‘unexpected }’ so I am really lost!

Can someone please explain what I am doing wrong, what I am missing, or if there is a better way to achieve what I want?

*Note that yes I did change the old code to reflect the proper path to content.php in TwentyTwenty. And yes, I am using a child theme.