One subsite on WP Multisite is showing: The theme directory "twentytwentyfour" does not exist.

One subsite in my multisite is encountering this issue. Switching to the [twentytwentyfour] theme does not resolve the problem. How should I handle this?

Code added to the subsite’s wp-config.php:

define('DB_NAME', 'siteAdatabase');
define('DB_USER', 'siteAuser');
define('DB_PASSWORD', 'siteApassword');

define( 'CUSTOM_USER_TABLE', 'wp_users' );
define( 'CUSTOM_USER_META_TABLE', 'wp_usermeta' );
define( 'COOKIE_DOMAIN', 'xxx.com' ); 
define( 'COOKIEHASH', md5( 'https://xx.com' ) ); 

All other default defines included with WordPress are identical between the subsite and the main site.

Code added to the main site’s wp-config.php:

define('WP_ALLOW_MULTISITE', true);

define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', false );
define( 'DOMAIN_CURRENT_SITE', 'x.com' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

const COOKIEPATH           = '/';
const SITECOOKIEPATH       = '/';
// Make admin cookies work across all subdirectories
const ADMIN_COOKIE_PATH    = '/';

define( 'COOKIE_DOMAIN', 'x.com' ); 
define( 'COOKIEHASH', md5( 'https://xx.com' ) ); 

The error is already quite clear: the theme directory twentytwentyfour does not exist. Try switching to a different theme.