I'm not sure if it's the JDK.

Looks like Tomcat's org.apache.tomcat.util.bcel is unable to parse the module-info from several of:

• your libraries (like FastInfoset-1.2.15.jar, txw2-2.3.1.jar, istack-commons-runtime-3.0.7.jar)
• and some of the Hibernate dependencies (such as byte-buddy-1.9.5.jar, jaxb-runtime-2.3.1.jar).

I suspect this has nothing to do with the Hibernate upgrade since the first ones would fail even without it? Very likely your Tomcat (bcel) needs to be upgraded to deal with the new modules metadata, which is not a specific problem of Hibernate but of all recently updated libraries.