_ is not on the classpath of project _, only syntax errors are reported

Every time I try to create a package for my java classes so I can finish my projects for school, errors like this occur:

When I finally try to run the program, I get an even more infuriating message:

It hurts me to be unable to properly test my code, even if I know I did well. It has been giving me anxiety for quite a while now, so I'm quite surprised this has slipped under the radar for so long.

• Operating System:
  

• JDK version: 15.0.2

• Visual Studio Code version:
  

• Java extension version:
  
  

Steps To Reproduce

1. Create a java class with methods and everything.
2. Put it in a folder with a test program.
3. List the folder as a package in both programs.
4. Try to use the class and it's methods in the test program. Both errors should be clearly visible by now.

Here is my code as an example of what can cause it. Try compiling either Test.java or Customer.java and it should be quite apparent.
Chapter10.zip

Current Result

A warning that constantly results in weird compiler errors

Expected Result

A working class that I can use

Öffnen Sie zunächst die angehängte Chapter10.zip und reproduzieren Sie den Bericht mit Test.java und Customer.java in VS Code unter Verwendung von JDK 15.0.2. Überprüfen Sie, wie die Java-Erweiterung die Einrichtung von package und classpath handhabt. Als erledigt gilt die Aufgabe, wenn die classpath-Warnung behoben ist und die Beispielklassen wie erwartet kompiliert werden und laufen.