I solved the issue.  Apparently even though my system was setup to use Java 17, I still had Java 11 available.  My /etc/default/tomcat9 file didn't explicitly specify JAVA_HOME.  So apparently XWiki just picked Java 11 rather than use the system's active version of Java.

I added the line `JAVA_HOME=/usr/lib/jvm/java-1.17.0-openjdk-amd64` and now it's working.