_ 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

Start by opening the attached Chapter10.zip and reproducing the report with Test.java and Customer.java in VS Code using JDK 15.0.2. Check the Java extension's handling of the package and classpath setup. Done means the classpath warning is resolved and the example classes compile and run as expected.