A few years ago the LTS after 17 was supposed to be Java 23, but it has since been modified, and the LTS releases went from every 3 years to every 2 years. Java 21 is definitely a LTS.
@@SunKing2, a clarification: JDK and Java do not have LTS anymore. The vendors have LTS releases and will probably follow Oracle LTS's choice of 21, 25, 29, and so on. It's a slight distinction but essential.