where is view state is stored

In the same location I told you when you asked the question here[^]. It hasn't changed

In hidden field the value is stored

View State stored the value of page controls as a string which is hashed and encoded in some hashing and encoding technology. It only contain information about page and its controls. Its does not have any interaction with server. It stays along with the page in the Client Browser. View State use Hidden field to store its information in a encoding format.
Suppose you have written a simple code , to store a value of control:

ViewState["Value"] = MyControl.Text;

Now, Run you application, In Browser, RighClick > View Source ,
look at the value. looks likes a encrypted string.(This is Base64 Encoded string, this is not a encoded string. So it can easily be decoded.)