Screenshot of the error
Error details
There is no topic as described in the screenshot of RVIZ. The topic /unicycle_bot_robot_description does work, but only after you enable the robot_state_publisher_node. In the first part to see the model you need to go to /home/simulations/ros2_sims_ws/src/unicicle_robot/unicycle_robot_pkg/urdf/unicycle.urdf. The topic /robot_description doesn’t work.
Note: there is a lot of inconsistency with the name of the robot. The Topics available call it unicicle_robot, but the file is unicycle robot. The RVIZ2 screenshots claim the TF frames are unicicle, but the actual TF frames are unicycle. They should all be unicycle. In the instructions even says uniclicle_base_link, which is wrong in yet another way.
Small issue: “it’s” should be “its”, unless it is a contraction of the words “it + is”.