NIC not working on Ubuntu server with GUI

When you installed the server addition, networking was handled by netplan. You have posted the relevant netplan file.

When you later installed a desktop environment, or GUI, Network Manager was installed along with all of its configuration files. NM and netplan are in disagreement as to who is responsible for networking. Let’s put NM in charge. From the terminal:

sudo rm /etc/netplan/*.yaml
sudo nano /etc/netplan/01-network-manager-all.yaml

Add the following:

# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager

Netplan is very specific about indentation, spacing, etc., so proofread carefully twice. Save (Ctrl+o followed by Enter) and exit (Ctrl+x followed by Enter).

Reboot and tell us if there is any improvement.