I would like to know whether there is an officially-mandated or recognized C/C++ Package Manager.
As @peterh describes in a comment, neither C nor C++ have an official package manager for libraries, modules or headers. This is dissimilar from languages like Rust (with the Cargo package manager) or Ruby (with Gems).
Also, C and C++ are very different languages, despite their having common "ancestry", and I would not conflate managing packages for both of them ... although others don't necessarily share my opinion on the matter.
Finally, C++20 will introduce modules into the language, creating an entirely new space of potential packaging of C++ artifacts - but which obviously has not yet been developed and explored.
See also this question here on the site regarding non-official C++ package managers.