org.freedesktop.Sdk.Extension.openjdk is a PR open since Apr 21 regarding this topic:
In the README of this repo is mentioned
OpenJDK 17 is the current latest version. This is not a long-term support (LTS) version and will be periodically updated as new JDKs are released.
Java 18 was published in March and Java 19 in Sept 22.
Are there maintainers of this package here? If not, how can we help to get this version shipped?
If you’re interested, we could help in maintaining this package.