The relevant type is "blob". There is no further structure. If the function that accepts void* is trying to extract structure out of the blob, there is a bug in that function and the type checker should already catch you trying to extract structure from something that isn't there.

> I mean WHY are you making an API that takes such a pointer to an unknown type to begin with?

It's not unknown in any meaningful sense. It is known to be a sequence of 'arbitray' datums of a given length, which is the exact type of input required for the scenario given.

As the article explores, some argue that you should define that sequence with a concrete type, but the article states that it doesn't offer any additional value as is posits that void* already communicates the same. In other words, it suggests that void* is the concrete type for that type already.