It doesn't for now, and doesn't really need to. Scala 3 isn't out yet, and when it is there will be a migration period (as always) while things will remain backwards compatible and libraries will remain cross compiled.
This book also explicitly skips over all the deep language esoterica, in order to focus on use cases. As a happy consequence, I expect ~all code samples to continue working unchanged in Scala 3 for the foreseeable future.
