The following snippets should help you disable commenting within WordPress.

disable-wordpress-commenting.php

<?php

// Disable Commenting in WordPress
// https://endurtech.com/how-to-completely-disable-comments-in-wordpress/

add_action( 'admin_init', function ()
{
	// Redirect any user trying to access comments page
	global $pagenow;
	if ( $pagenow === 'edit-comments.php' )
	{
		wp_safe_redirect( admin_url() );
	exit();
	}
	// Remove comments metabox from dashboard
	remove_meta_box( 'dashboard_recent_comments', 'dashboard', 'normal' );
	// Disable support for comments and trackbacks in post types
	foreach ( get_post_types() as $post_type )
	{
		if ( post_type_supports( $post_type, 'comments' ) )
		{
			remove_post_type_support( $post_type, 'comments' );
			remove_post_type_support( $post_type, 'trackbacks' );
		}
	}
});
// Close comments on the front-end
add_filter( 'comments_open', '__return_false', 20, 2 );
add_filter( 'pings_open', '__return_false', 20, 2 );
// Hide existing comments
add_filter( 'comments_array', '__return_empty_array', 10, 2 );
// Remove comments page in wp-admin menu
add_action( 'admin_menu', function ()
{
	remove_menu_page( 'edit-comments.php' );
});
// Remove comments links from admin bar
add_action( 'init', function ()
{
	if ( is_admin_bar_showing() )
	{
		remove_action( 'admin_bar_menu', 'wp_admin_bar_comments_menu', 60 );
	}
});

?>