Network manager applet shows 'not connected', and one unmanaged Wired connection, internet working

Question

I have no experience configuring network manager by text configs, used only GUI. When moving mouse over NM tray icon there are tooltip "Not connected", however I see one connection then clicking it - "Wired unmanaged". Internet working fine.
I make new ethernet connection with priority 10 but it not appear in NM applet menu.

leonid@DevSSD:~$ cat /etc/network/interfaces 
# ifupdown has been replaced by netplan(5) on this system.  See
# /etc/netplan for current configuration.
# To re-enable ifupdown on this system, you can run:
#    sudo apt install ifupdown

leonid@DevSSD:~$ cat /etc/netplan/01-netcfg.yaml 
# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
  version: 2
  renderer: networkd
  ethernets:
        enp3s0:
            dhcp4: true
            dhcp6: true
            nameservers:
                addresses: [127.0.0.1,127.0.0.53]
                search: [JR]

Question is: how to connect by new created ethernet connection, or at least make "wired" connection managed?
Ubuntu 18.04 cinnamon

Answer 1

Set /etc/NetworkManager/NetworkManager.conf back to:

managed=false

Set /etc/network/interfaces back to:

auto lo
iface lo inet loopback

Change /etc/netplan/01-netcfg.yaml:

Rename 01-netcfg.yaml to 01-netcfg.yaml.HOLD for backup purposes.

sudo mv /etc/netplan/01-netcfg.yaml /etc/netplan/01-netcfg.yaml.HOLD

Create a new file called /etc/netplan/config.yaml...

sudo -H gedit /etc/netplan/config.yaml # create/edit a new file

or

sudo pico /etc/netplan/config.yaml # create/edit a new file

with the following content:

network:
  version: 2
  renderer: NetworkManager

sudo netplan generate # generate new config files

sudo netplan apply # apply new configuration

reboot # reboot the computer

Use the standard NetworkManager menu to configure your "Wired Connection".

Verify Internet operation.

Answer 2

I had the same problem on Ubuntu 22.10 server with Unity based Cinnamon desktop.

I did as follow (based on @heynnema's answer):

• /etc/network/interfaces did not exist, so I created it with inside:

  auto lo

  iface lo inet loopback

• I did'nt found 01, but 00-netcfg.yaml instead in /etc/netplan/.

I just edited it as by adding "renderer: NetworkManager":

(other devices not used yet - only one is dchp for internet)

network:
  ethernets:
    enp2s4f0:
      dhcp4: false
    enp2s4f1:
      dhcp4: false
    enp3s6f0:
      dhcp4: false
    enp3s6f1:
      dhcp4: false
    enp7s0:
      dhcp4: true
  version: 2
  renderer: NetworkManager

With as results for all of my devices after the netplan apply command: