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 Personally, I enjoyed the lectures of https://rust-class.org/, though the Rust code itself may be a little outdated (it's from 2014).
Microkernels are not really modern as such. Just different.
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.