Generally speaking the “default_config” refers to a key/entry in your configuration.yaml file, unless you’ve removed it it is there by default… nothing else to do. Some folk like to remove it and add system configurations back in manually, I think it is a pointless exercise and just causes problems down the road.
If you just want to start using packages then it is not something you need to get hung up on. Check that your configuration.yaml file has the key “default_config:” (it is actually the first line in my configuration.yaml file) and carry on.
Personally whenever I read “default_config” I ignore it and move on.