I just saw that you're using 4.0. You do realize that 4.0 is not even alpha stage yet?
You should only be using 4.0 if you are a developer who is working on it, or if you are testing and helping to find bugs/issues for those developers. Many things don't work right now, and many others have changed from 3.x in ways that are not yet documented.
If you want to try and help with 4.0, you will need to follow the issues and discussions on Github, where you will find what has been changed. For example, GDScript has been changed a great deal, including many keywords becoming annotations, such as
onready. Some of the changes are summarized here:
Again, I can't recommend this more strongly: If you're a beginner, you should not be using 4.0.