If you get the following message on your Magento backend.
Magento 2: “Your web server is set up incorrectly and allows unauthorized access to sensitive files. Please contact your hosting provider”

Follow instructions in references below. If the problem persists, open /etc/nginx/sites-enabled/example.conf and add:

location ^~ /app/etc {
return 404;
}

restart nginx.
References:

1. https://magento.stackexchange.com/questions/101469/magento-2-your-web-server-is-set-up-incorrectly-and-allows-unauthorized-access
2. https://www.mageplaza.com/kb/your-web-server-set-up-incorrectly-allows-unauthorized-access-sensitive-files-magento-2.html