Please note that we are talking about installing a new server, not a migration from 6 to 7.We tried to convey it quite explicitly in the upgrade how-to, and that how-to is heavily recommend getting read and followed closely before and during upgrade, to avoid as many pitfalls on the way.
But we'll see if we can further improve this, possibly adding a hint to thepve6to7
checker script.
I think that it would be a VERY helpful and good idea for the Proxmox install script to just clone the physical NIC's MAC on the bridge interface, when doing the initial install/setup.
Or maybe add a bolded text phrase on the install UI -> Network setup page, where is mentioned that one should clone the NIC's MAC address to the bridge interface after installation if there's no network connectivity.
This will help Proxmox avoid a ton of future topics (like mine) from users that are MAC-restricted by their ISP (which is basically 90% of ISPs I guess?).