It will be easy to understand if to represent the function declaration

void* volatile* (*func(unsigned long const long volatile int, signed, long*[*][42]))(__int128* (*) (int* restrict const[static restrict const 17]));

using typedefs.

The first one can be the following

typedef _int128* FunctionAsParameter(int* restrict const[static restrict const 17]);

The second one is the following

typedef void* volatile* FunctionAsReurnType( FunctionAsParameter * );

And at last teh original function declaration will look like

FunctionAsReturnType * func( unsigned long const long volatile int, signed, long*[*][42])'