Ubuntu installs a config file that sets most devices unmanaged:

/usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf:

[keyfile]
unmanaged-devices=*,except:type:wifi,except:type:gsm,except:type:cdma

To disable this, You can create a blank file with the same name in /etc:

sudo touch /etc/NetworkManager/conf.d/10-globally-managed-devices.conf
sudo systemctl restart NetworkManager