Is there any protocols to identify what sort of document MS-408 is?

[ololololo]

Do you think a document that has repeatable words at the rate of the MS-408 borders on gibberish?

It depends on what kind of repetitions you mean. They are found in all languages and are not something supernatural.

Can we agree it's a conlang with low entropy, yes or no?

We can't, because no one has provided convincing evidence or an example of a similar language.
If Voynichese is an artificial language, it is likely to be linguistically incomplete (i.e., you may not be able to use it to communicate with people or describe your day) and functional (i.e., designed to describe what is depicted in the book).

Many have reported it does not behave like a normal language, if it's constructed, it does not have to follow other language rules

No one has canceled the banal encryption