I am getting a compiler error when attempting to run the game within the default project.
As mentioned in the course title and the intro, the course is for Godot 3, so you'll need to use Godot 3.5 LTS to open the files and follow along. You can download it here: https://godotengine.org/download/3.x/
Note that as you imported the project in Godot 4, its files got converted and won't open in Godot 3 anymore. You'll need to re-download the course files to get a fresh copy and import it in Godot 3.