No internet connection after ubuntu server 20.04 install, ifconfig not available

Networking in Ubuntu server is managed by netplan. Your file lacks the details needed to connect the ethernet properly.

First, let's rename the file:

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

Now, let's change it to include the required details:

sudo nano /etc/netplan/01-netcfg.yaml   

Change the file to read:

network:
  version: 2
  renderer: networkd
  ethernets:
    ens33:
      dhcp4: true

Netplan is very particular about spacing, indentation, etc. Proofread carefully twice. Save (Ctrl+o followed by Enter) and exit (Ctrl+x) the text editor. Follow with:

sudo netplan generate
sudo netplan apply

You should be all set.