As of WordPress 5.5, email notifications will be sent after each attempt to auto-update a plugin or theme regardless of outcome (success or failure).
If you are managing many sites, these email notifications might be annoying to you than useful.
The following snippet can be used to disable email notifications for themes and/or plugins auto-update:
add_filter( 'auto_plugin_update_send_email', '__return_false' );
add_filter( 'auto_theme_update_send_email', '__return_false' );
In case it helps, here’s how to add custom codes in your site: https://www.wpbeginner.com/plugins/how-to-easily-add-custom-code-in-wordpress-without-breaking-your-site/
That’s it. Thank you!