I'm not sure if this one is a bug or a new feature...
In 5.x, we can only use Hibernate Criteria on a Stateless session, not JPA criteria.
In 6.0, Hibernate criteria are gone, so we cannot use any form of criteria on a stateless session, only string-based queries. This is especially problematic for integrations that rely on the metamodel to build queries automatically, such as the mass indexer in Hibernate Search.
The criteria builder can be accessed through the session factory, so it's not a big deal that there is no getCriteriaBuilder() method on StatelessSession. What's really missing is the createQuery(CriteriaQuery) method on StatelessSession.