Lxd network set says: error: unknown command: network

why lxc network command doesn’t work?

lxc network set lxdbr0 ipv4.routes

You’re likely using LXD 2.0.x which doesn’t have the network API.

I just upgraded to 2.18 and did systemctl restart lxd and am having the same problem. Does something else need to be done following the upgrade ?? lxd --version shows 2.18

You need to have both the “lxd” and “lxd-client” packages upgraded, it may be that you’re using the 2.0.x version of the command line client which wouldn’t know about the “network” subcommand.