For further info, if anyone is interested, Stephen Bax claimed a decade ago to partially decode the manuscript; here’s a video with his reasoning, as well as the paper he released. Sadly Bax passed away in 2017 (may he rest in peace), so the work was left incomplete.
That is part of the mystery for sure. If it is a modern - or at least later - hoax it’s the work of the best forger in history. All physical and historical evidence points to it being created in the first half of the 15th century. It also points to multiple people being involved in making it. And the complicated rules and structures of Voynichese involve an awful lot of effort for a medieval scam.