There's been a recent update to the proposed syntax & semantics, as indicated by the date on the JEP.
When I noticed the "preview feature" wording I went and tried running it with --enable-preview on a mainline OpenJDK build, but value records still didn't compile, and then I went back and saw that that wording has been on the JEP for some time.
There are also more up-to-date Valhalla builds available at builds.shipilev.net, but I'm not sure if there's some specific reason they haven't updated the EA page in years or if it's just not a priority.
When I noticed the "preview feature" wording I went and tried running it with --enable-preview on a mainline OpenJDK build, but value records still didn't compile, and then I went back and saw that that wording has been on the JEP for some time.
There are also more up-to-date Valhalla builds available at builds.shipilev.net, but I'm not sure if there's some specific reason they haven't updated the EA page in years or if it's just not a priority.