The lessons in that book have broadly held true for nearly every single one of my employers throughout the entirety of my career.

Indeed a lot of things have changed. A worthwhile exercise is to read the book, contemplate how things have changed, and try to map lessons from the book onto modern technology and organizational practices. A LOT of the core principles are still relevant IMO, even if many of the implementation details are not.

Your comment and the OP both mention some things that are outdated about the book. What are those things?

Our field is full of vague, terrible opinions and useless advice. Arrogant people that think they're better than others.

That book isn't, it's built from humility and a rare bright light in this god forsaken field.

So men and months have suddenly become fungible ?

You should tell these AI companies and we could have AGI tomorrow if only they would throw a few thousand more men on the project.

Or perhaps today's men are coding agents? You can spin up as many agents as you care to, so asymptotically any project should be completable in zero time, regardless of complexity.

IMHO, Brooks's Law applies more today than ever.