The book doesn't explain how to setup scala3 at all, it assumes you know how to install programs which is fine, but the scala-lang website is also failing at educating others on how to install scala3, only showing how to install scala3-repl and scala3-compiler.
The first real coding exercise of the book instructs the reader to create a basic script and invoke scala on it, however the sbt and Coursier tooling do not provide a scala v3 binary, only scala v2 via cs's "setup" command. This scala v2 binary cannot execute the simple @main function that's written for the reader to recreate. There's various StackOverflow, GitHub and other places filled with confusion and frustration and not much assistance on actually getting the code to run.
Literally the hello world example cannot be ran out of the box. You can get around this if you stay in the REPL and just :load your code, I found this after several googling attempts.