Hi,
It seems that there is an issue with Snap on Ubuntu 18. The current solution is to check out a pre-Snap commit on the robot-config repo. The rest of the setup guide remains the same.
Could you try this block of code instead of the one specified in the guide?
git clone https://github.com/husarion/robot-configs
cd robot-configs
git checkout 47f1309
cd ..
sudo ./robot-configs/install.sh
rm -rf robot-configs
sudo setup_robot_configuration rosbot_xl ros2_humble
If the issue persists, please let us know.
Stefan