http://cr.openjdk.java.net/~dlsmith/jep8277163/jep8277163-20220519/specs/value-objects-jls.html

8.1.5 Superinterfaces

...

It is a compile-time error if an identity class (8.1.1.5) has a superinterface that is a value interface, or if a value class has a superinterface that is an identity interface, or if any class has both an identity superclass or superinterface and a value superclass or superinterface.

But javac tolerates this code:

identity interface II {}
value interface VI {}

abstract class X implements II, VI {}