your g/w is a router/modem or pfsense ?
verify your g/w configuration and any outbound traffic is blocked ?.
Any iptables/firewall configured on your Proxmos VE or G/w ?
My mind is boggled: what can possibly explain internet access, while not allowing connections to be set up from proxmox server and containers, while the rest of the network can do so just fine through a proxmox (OPNsense) VM?
