Is it possible to use an instance as gateway in a ovn network?

Late reply, but I got it working:

project: default
name: moonpie-vlab
description: ''
type: ovn
config:
  ipv4.address: 192.168.40.1/24
  ipv4.dhcp: 'false'
  ipv6.address: none
  network: none

You have to set the ipv4.address field to be the ipv4 addresses you are giving out from the router. But it is the router vm/container doing it.

My thread here: OVN but with a firewall VM as the uplink? - #2 by moonpiedumplings