Partially solved… If I delete the vlans in incus admin os system network edit (apart from vlan.lansrvs) I can then follow the procedure from this post to make a physical managed network and then just attach it to my instance with network: <example_vlan>.
If I do this with say a Debian container then run dhclient it does successfully grab an IP.
It looks like though I’m running into the issue here where I want the OCI container (in this case Frigate) to use DHCP on a second interface so that it can actually make a connection out to my cameras. I don’t really want to assign a static IP here as I have a DHCP server in charge of the entire subnet (and there are other containers I want to set up across multiple subnets like this). Is there any workaround, for example somehow having Incus negotiate the IP and then use it to attach to the container as a routed type nic?