No, it’s not. It is unknown. To say it may be unknowable you need a fundamental reason why it may not be knowable.
What lies behind event horizons may be unknowable. We have theoretical reasons to suspect this. What LLMs are doing isn’t well enough understood, theoretically, to even say what is knowable versus unknowable. Just what is known and not.
A method not existing and a method being impossible (or unlikely) to exist are separate concepts. When you say something is unknowable, it should mean it literally cannot be known—route around the question entirely.
I had gotten my wires crossed and thought the OP was asking about a specific situation, but it was actually a question about the general pattern.
A specific situation will often pass before any theoretical tools can be found that could possibly answer the question.
For a general pattern, though, you're entirely right - if the tools arose hundreds of millions of years from now, that range of questions becomes answerable, and the information is then knowable.