Swift build generic type at runtime

Swift 5.1
Suppose I'm deserializing some data. I'm interested in reconstructing the exact same types as were serialized, but some may involve generics. Consider the following example case.

let layers = 4
let value: Int64 = 17

var output: Any

???SOMETHING???

print("\(type(of: output))") // "Optional<Optional<Optional<Optional<Int64>>>>"

Is there a way to get an output with a runtime type of Optional<...Optional<Int64>...>, where the number of nested layers of Optional is equal to layers? (And doesn't rely on e.g. hard-coded case statements full of classes.) Perhaps reflection, some type initializers I don't know about, maybe some black magic use of pointers or object_setClass or something?

I would also accept strong evidence that it is fundamentally impossible in Swift, such as documentation stating that every specification of a generic class used in a program is generated individually at compiletime, and therefore you cannot newly specify a generic class at runtime. ...Though even in that case, it might still be possible, considering things like Java's ClassLoaders.