How to correctly setup Ubuntu 18.04 LTS installed from mini.iso to use NetworkManager?

To transform the system to normal MATE one should:

Remove systemd-networkd renderer:

sudo rm -v /etc/netplan/01-netcfg.yaml
sudo rm -v /etc/netplan/50-cloud-init.yaml

Restore Network Manager renderer:

cat <<EOF | sudo tee /etc/netplan/01-network-manager-all.yaml 
# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager
EOF

Apply netplan configuration with:

sudo netplan apply

Restart NetworkManager

sudo service network-manager restart
sudo service NetworkManager restart

Optionally restore contents of /etc/network/interfaces

cat <<EOF | sudo tee /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
EOF

Note: this method is also applicable to Ubuntu MATE 20.04 LTS, 21.04 and 21.10.