Is anyone even using such declarations?

not really, the worst you'll see is function pointer declarations.

well, simple ones like this
int (*someFunc(char *blah, int blah2));

I always see comments like this on Jow Forums. I don't get it, are you trying to anonymously hint to your anonymous friends that you have a job? Because shit like this and much worse is written everywhere in every codebase I've ever worked on.

Only three and four star programmers do, so yeah, real programmers do this

Shouldn't it be int (*someFunc)(char* blah, int blah2);

I cast everything as void*

that looks worthy of compsci meme degree

I just finished that chapter.

It should

Generally expressions this complicated are either rarely used or not used at all (because there's an easier or simpler way to do something). One of the more common things you're likely to see is an array of function pointers, or an array of pointers to arrays of function pointers. An array of pointers is a fairly common solution to having the program do different things based on an index or state value, instead of using a lot of if statements or a case statement, etc
The book defines these because someone inevitably will use them, and it's important to have a consistent way to identify and read them

meanwhile in Rust
fn x() -> &[fn() -> char]
let x: [fn() -> &[char; 5]; 3]
C declaration syntax was a mistake

>C declaration syntax was a mistake
Nah, only function declarations and expressing return types. If it had been done name(parameters) -> return type instead, then nested function pointers wouldn't be such a convoluted mess.

Almost never, and if they ever would, they'd clean it up using typedefs.

The whole idea of declarators is brain damaged and backward too.

organizing your function calls in arrays is often used in compiller programming and game development where you can have a shitload of calls and you use enums as array indexes.