Ubuntu Server and Ubuntu Desktop use different network managers. Ubuntu Server uses networkd which doesn’t have a GUI component. So after adding a desktop to Ubuntu Server you won’t be able to see or change the configuration via the GUI by default.
For you to be able to see the network settings on the GUI you need to switch from networkd to NetworkManager.
apt install network-manager network-manager-gnome network-manager-openvpn network-manager-openconnect network-manager-openvpn-gnome
Check which systemd network daemons are active:
systemctl list-unit-files | grep -i network
Disable/stop networkd services:
systemctl disable systemd-networkd.service systemctl disable networkd-dispatcher.service systemctl stop systemd-networkd systemctl stop systemd-networkd.socket systemctl stop systemd-networkd.service systemctl stop network-dispatcher.service
Remember that nmcli can be used for CLI NetworkManager control also.
Network interfaces are listed in yaml files in /etc/netplan/
and add a line after the version: 2 entry to be renderer: Networkmanager
network: ethernets: eno1: dhcp4: true version: 2 renderer: NetworkManager
Check the changes and apply them:
netplan generate netplan try / netplan apply