@worldsendless Mine is from 2020 (PHP 7.4), and is the most recent one I'm aware of.
https://leanpub.com/thinking-functionally-in-php/
The changes since that would impact FP are Enums and readonly properties. The rest is still largely valid. (I'm hoping we can get more features into the language that would force me to write a new edition.)
Also check out https://github.com/Crell/fp/ , which I built sometime after writing the book.
@worldsendless There's a number of very cool improvements to the language, yes. Whether they impact the FP story is the question.
Enums are new. Readonly makes value objects easier, as does constructor promotion. The mixed type is nice in a few cases. Union types don't matter for FP, and neither do attributes.
The core FP story hasn't really changed in the last 4 years. Had any of the FP based RFCs I submitted passed, that would be different, but... They all got blocked.