I would like to know
my goal question
First, if you want to have total control of your updates, and you want to be sure that your WP website only updates when you or your developers wants, you need to add the following filters and constant to stop the automatic updates:
In your wp-config.php add this (for the core updates):
define( 'WP_AUTO_UPDATE_CORE', false );
In the functions.php add this (disable automatic WordPress plugin updates):
add_filter( 'auto_update_plugin', '__return_false' );
and this (disable automatic WordPress theme updates):
add_filter( 'auto_update_theme', '__return_false' );
After that, you will be able to know when the updates happens since it's all controlled by you (and/or your developers).
Another (not always reliable) way to check when an update happened is by checking the versions. You can then verify when a (WP, plugin or theme) version was released.