There is no support for Java 17 yet. The plan is to add it in Cassandra 5.0 [1]. By default, builds are done with Java 8. You can build with Java 11 by setting the flags documented on the site [2]. Cheers!
[1] https://issues.apache.org/jira/browse/CASSANDRA-16895 [2] https://cassandra.apache.org/_/development/ide.html