DId you restart the Apache webserver? As far as I'm aware, restarting the webserver is required to apply the updated setting. You can do that like this:

systemctl restart apache2

By default, the permissions should be as required for this to "just work". Although if you have manually made changes to files/directories within the WordPress root (/var/www/wordpress) such as manually creating the file/directory, please ensure that it is owned by the 'www-data' user (the webserver user). It sounds like you may have already done that, but just in case, to ensure that all the WordPress files are owned by the webserver, you can run this:

chown -R www-data:www-data /var/www/wordpress

If you have already followed those steps, and it still doesn't work as expected, please let me know and I'll see if I can get it to work as it should on a test server.

It may also be worth checking the Apache logs (/var/log/apache2) as they may contain some hint to what the issue may be?

Alternatively, if you have managed to fix it yourself (or do), please post back with whatever was required. That way the info will be available for others. Also, if there is a tweak that we can pre-configure to improve the appliance out of the box, then we'll do so.

FWIW it appears that even when it's configured correctly, despite the "debug" name, it won't actually log anything unless there is an error (although perhaps that's configurable?). I launched a test instance and configured my wp-config.php as per your notes:

// WordPress debugging mode (for developers).
define('WP_DEBUG', true);

// Enable Debug logging to the /wp-content/debug.log file
define( 'WP_DEBUG_LOG', true );
//define( 'WP_DEBUG_LOG', 'wp-errors.log' );

// Disable display of errors and warnings
define( 'WP_DEBUG_DISPLAY', false );
@ini_set( 'display_errors', 0 );

// Use dev versions of core JS and CSS files (only needed if you are modifying these core files)
define( 'SCRIPT_DEBUG', true );

And as you noted, there is no log file being created. However, when I added a line to the default (twentytwenty) theme, like this:

echo "error_log('Debug log loading');" >> /var/www/wordpress/wp-content/themes/twentytwenty/functions.php

Then I restarted Apache:

systemctl restart apache2

And reloaded the home page in my web browser. Then guess what? The debug.log file gets created! And it contains the message inserted into the theme! :)

root@jed-test-wordpress ~# find /var/www/wordpress/ -type f -name "*log"
/var/www/wordpress/wp-content/debug.log
root@jed-test-wordpress ~# cat /var/www/wordpress/wp-content/debug.log
[27-Jan-2021 08:00:01 UTC] Debug log loading