Kubuntu networking configuration file

I've always been a GTK camp user but switched to Kubuntu just recently (for 20.04). But I haven't found where Kubuntu store its networking configuration files yet. I've looked at every file that I know of, e.g.:

$ cat /etc/netplan/01-network-manager-all.yaml
# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager

$ dir /etc/NetworkManager/system-connections/
total 0

$ cat /etc/network/interfaces
cat: /etc/network/interfaces: No such file or directory

The reason I'm asking is that I want to use Static IP for my Kubuntu, but I don't know where do I start with. thx.