Where is Ubuntu 20.04 default network configuration?

Your established connections can be found in the following directory:

/etc/NetworkManager/system-connections

Here, you will find an individual file for each known connection.

Unless your IP is static, the IP will not be listed in the file as the IP will be assigned dynamically by DHCP through your router. Also, you need root permission to read these files so a simple grep may not suffice unless you use sudo grep.

When you set up everything through NetworkManager using the GUI, these files will create automatically. However, you can edit these files manually but you will need to restart NetworkManager after making any changes using sudo systemctl restart network-manager. You can also set up a connection using nmcli but that’s another story.

There are more parts to your network like DNS that are setup with other files in other places depending on what you use for DNS but again, that’s another topic.