@jota does the code in uppercase differ from the one in lower case?
is define( 'WP_AUTO_UPDATE_CORE', false ); the same as define( 'wp_auto_update_core', false ); ??
I do not know if the uppercase and lowercase variables differ in WordPress, but I suggest you use the same syntax that the official documentation of WordPress mentions.
In the situation, case does matter. define() is a core PHP function that defines a Constant. So in this use case WP_AUTO_UPDATE_CORE should be capitalized. https://www.php.net/manual/en/function.define.php helps to explain this.
It's also worth noting that Wordpress uses all caps for it's constants, so when it looks for WP_AUTO_UPDATE_CORE it won't find it if it is defined as wp_auto_update_core
Hope this helps,Ron