Whether to open the firewall for the ports in services.deluge.config.listen_ports. It only takes effet if services.deluge.declarative is set to true.
It does NOT apply to the daemon port nor the web UI port. To access those ports securely check the documentation https://dev.deluge-torrent.org/wiki/UserGuide/ThinClient#CreateSSHTunnel or use a VPN or configure certificates for deluge.