Just a small tipp for those who are using 3.1 to follow this course.
GDScript has a keyword named class_name which allows to register a global class name for a script.
I used this for the CombinationGenerator like this:
class_name CombinationGenerator extends Node
static func generate_combination(length):
var combination = []
for number in range(length):
randomize()
combination.append(randi() % 10)
return combination
which then allows me to just do
func generate_combination():
combination = CombinationGenerator.generate_combination(combination_length)
in Computer.gd, as it is globally accessible thanks to class_name. 