Hi, @jhnd7710
Got it. So, the Mattermost app that you installed through the Ubuntu Software is actually the desktop app instead of the actual Mattermost Server.
The config.json is only configurable in the /opt/mattermost/config/config.json when you as the System Administrator, deploy and install Mattermost Server.
Are you the end user or an admin who is trying out Mattermost on your organization?