Hello Dav2 - I admit I am a bit confused by Matrix asking if you've a public IP.
As I understood it, 'by default' at install you provide a private IP to the proxmox host.
PVE then emulates a 'virtual switch' - the bridge in software.
This bridge allows the guest VMs to connect to the network at the same level as the host.
For example, if the host is on (network) 10.10.10.0/24, and a guest is connected to the bridge then for all intents and purposes the guest is ALSO on 10.10.10.0/24
And would - if such a service were running - pick up a DHCP address or use a static configuration.
I don't pretend to understand why the guest cannot connect to the wider network. I am having the same issue myself and I want to understand where I'm going wrong.
I admit I am complicating things by using VirtualBox with a Bridged interface but this is down to not having spare hardware to put PVE on (yet).