Java25: Compact file in subfolders give package error

Problem: I have installed Terurin JDK25 and Eclipse JDT Eclipse Java Development Tools 3.20.400.v20250923-2045 org.eclipse.jdt .
When I create a compact source file in the root directory of my Java project, with only a main(), there is no error reported in Eclipse. But if I create a compact source file in a subfolder (package), the JDT compiler give me an error about a missing package declaration (see picture)

Expected: Eclipse should not give an error for compact source files in subfolders about missing package declaration and should let the program be run without error.

I am a teacher and I want to use compact source file to simplify the writing of Java programs for my students, but I want to be able to put the programs of each chapter in a different folder, and I think Eclipse should let me do that.

Thanks
Nicolas