For instance the chapter on web servers is far from today's best practices. It only mentions Apache http (nowadays Nginx is much more widespread), gives an advice about a default configuration which is no more default, and mentions a path that has changed in recent Debian installs. Even considering its age, the quality of this chapter is dubious: it forgets important points, like disabling .htaccess and directory listing, removing unused modules...

Modern tools are obviously missing from this guide: apparmor (though it was in use in 2017), nftables, systemd (unit settings that prevent /home access, prevent privilege escalation, etc)...