all starts from here:
https://stackoverflow.com/questions/59209739/org-hibernate-mappingexception-composite-id
they solve the issue using @IdClass and it works !
problem:
it works with 5.4.10.Final:
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-entitymanager</artifactId>
<version>5.4.10.Final</version>
</dependency>
but it definitely fails with 6.0.0.Alpha4:
<dependency>
<groupId>org.hibernate.orm</groupId>
<artifactId>hibernate-entitymanager</artifactId>
<version>6.0.0.Alpha4</version>
</dependency>