What port do I need to forward on my upstream router provided as my cable modem to my Beryl in order to configure DDNS?
DDNS itself is just IP resolution to your public IP.
So depends on which service you want to access, you need to set up different port forward.
If you want to access router UI, you can forward 8080 to the router’s IP and 80 port. So you can access ddns-ip-address:8080 to access the router
If you want to access router ssh, you can forward 2222 to router’s IP and 22 port, then you can ssh to ddns-if-address:2222