Thanks @modaltb , that worked! I had to set it to run as a background function using the &. It's running perfectly now.
I probably want to rewrite it as a task, but that example code looked tough to follow. I wish the PX4 developer manual included more step by step tutorials, like the ROS tutorials.
When doing firmware development or basic Flight Core setup with QGroundControl such as loading custom firmware I prefer to not need the Power Module. Unfortunately the USB connector on the Flight Core does not pass through the +5V so the board can't be powered by USB alone.
To fix this issue I hack into the provided USB cable and attach a second 4-pin connector to the +5V and Gnd wires that then can provide USB power to the CAN connector J8. See photos.
This is not ideal, but it gets the job done. I've asked Modal AI to consider making this cable themselves to sell or provide with the Flight Core kit.
I'm sure the concern is browning out the +5V from the USB.