First of all, great HOWTO, great work!
For everyone running Proxmox having hassio in in an own VM, the guide above will definitely work, but you will create a network assignment insight the VM instead of having it managed in Proxmox.
So if you like to have everthing maintained by proxmox, here my cents.
1.) Add Network Interface in Proxmox
2.) Connect to Hassio with SSH (use community SSH addon)
My config is simple, but I only activate it manually, so no issue.
Putty login by user and password specified.
A command like "login" is not required. When you are in, you are in and we can start.
3.) Check available devices and status
`nmcli device status`
In my case a device called enp0s18 is disconnected
4.) Enable enp0s18 by adding a connection name (HassOS-vlan) + DHCP
`nmcli con add type ethernet con-name HassOS-vlan ifname enp0s18`
In case you would like to have a static IP adress use (of course change it to your needs!)
nmcli con add type ethernet con-name HassOS vlan ifname enp0s18 id 10 ip4 192.168.10.220/24 ipv4.dns 192.168.10.254 gw4 192.168.10.254
5.) Check your IP Leases in your router if the Hassio came up with another interface, in my case a mikrotik router
6. To be on the safe side, ping hassio and open the website on the new IP adress
