I promise that this is a good-faith question: is MINIX still the best OS teaching tool? Personally, I enjoyed the lectures of https://rust-class.org/, though the Rust code itself may be a little outdated (it's from 2014).
'Best' is subjective, of course. If you think a pretty well written, accessible textbook coupled with a working, non-trivial but understandable codebase to examine is a good way to learn things, then "Operating Systems: Design and Implementation" and Minix is a pretty good choice. YMMV.
the foundational aspects of actually-used operating systems have been basically the same for 25 years or so. Lots of improvements, sure, but the basic ideas remain the same. MINIX3 is even kind of advanced compared to, say, Linux, since it uses a microkernel architecture. So it's as fine place to start as any.
Minix is a lot older than 25 years. Your point stands, but you need to increase the age. Minix and Tannenbaum's textbook was part of my operating systems class in undergrad CS. I think I took that class in 1989 or 1990.
