Hi Gabrio,
When Port Forwarding (and some more) is not in the Security Menu your ConnectBox runs so-called IPv6 DS-Lite Firmware. See attached image for the Menu you need.
Just call or Chat with Ziggo and ask for replacement by IPv4 Firmware.
https://www.ziggo.nl/klantenservice/contact/
After that, everything will look familiar again.
Regards, Han