"Rust 2018" is not a specific version of Rust. It's an edition.
Rust's current version is 1.63, released yesterday. Version 1.59 was released at the end of February, making it less than 6 months old. In my opinion, if you are still at the early stage of learning Rust, you won't miss much of the minor advanced features added since then.
Aside 25 minor, if major changes are what listed at left side here Introduction - The Rust Edition Guide at point 4, yes... a book covering rust 2018 is still enough updated.
I don't see deprecated code in rust 2021 vs rust 2018.
Is it planned to reprint the book to cover Rust 2021?
There is not much difference between editions. Editions are for allowing minor but technically breaking changes which would otherwise require a major version increment, and for allowing Rust code written using different editions to co-exist. Thus, Rust editions aren't deprecated.
Fun fact - if you won't have access to the internet but will still have a computer with you, you can still read the offline version of the docs via rustup.
$ rustup doc --help
rustup-doc
Open the documentation for the current toolchain
USAGE:
rustup doc [FLAGS] [OPTIONS] [topic]
FLAGS:
--alloc The Rust core allocation and collections library
--book The Rust Programming Language book
--cargo The Cargo Book
--core The Rust Core Library
--edition-guide The Rust Edition Guide
--embedded-book The Embedded Rust Book
-h, --help Prints help information
--nomicon The Dark Arts of Advanced and Unsafe Rust Programming
--path Only print the path to the documentation
--proc_macro A support library for macro authors when defining new macros
--reference The Rust Reference
--rust-by-example A collection of runnable examples that illustrate various Rust concepts and standard
libraries
--rustc The compiler for the Rust programming language
--rustdoc Generate documentation for Rust projects
--std Standard library API documentation
--test Support code for rustc's built in unit-test and micro-benchmarking framework
--unstable-book The Unstable Book
I don't think the printed book is out-dated at all, the changes since 2018 are quite minor and mostly outside the scope of the book. You can read about the changes introduced by the 2021 edition here: https://doc.rust-lang.org/edition-guide/rust-2021/index.html