Bounce Email via monitored gmail inbox does not work

is the PHP version the cron uses the same PHP version as the webserver uses? It seems like Mautic cannot connect.

You can also try to specify the right PHP in the cron like this:

/usr/bin/php7.3 /var/www/list.xxx.com/web/bin/console mautic:email:fetch

There are better ways to process bounces from Amazon. On Mautic SES Bounce Processing you can read about it.