My original Desktop Host installation 1) running simulated URDF Visualization using Gazebo and 2) Missing micro_ros_agent errors solved.
1) Launch error solved by rerunning the linorobot2 repository clone, rosdep and build commands in the colcon workspace. However to avoid a launch error, revise the command in 1.1b Using Gazebo to "~$ ros2 launch linorobot2_gazebo gazebo.launch.py. The gazebo.launch script is in the "linorobot2_gazebo" package.
The linorobot2 Gazebo and RVIZ Simulation with teleop works great and will now try a simulated XV11 Lidar (which I have the hardware for the Robot) & Depth Sensor simulation only, but will pursue getting my Oak-D-Lite to work. Hope the above is OK.