It's not a mental issue, it's just a rare thing that happens. Voynich fits the whole bill for the work of a naive artist.
It also applies to a range of natural phenomena, e.g. lunar craters and earthquakes: https://www.cs.cornell.edu/courses/cs6241/2019sp/readings/Ne...
So the fact that word frequencies in the Voynich Manuscript follow Zipf's law doesn't prove it's written in a natural language.
Not a recent hoax/scam, but an ancient one.
It's not like there weren't a ton of fake documents in the middle age and renaissance, from the donation of Constantine to Preserve John's letter.
Whoever made the document was sincere in making up something that doesn’t exist. They had no intention to mislead. You wouldn’t call a D&D campaign a hoax because it features nonexistent things?
I doubt it's a rulebook cause it's not a real language.
If it's a prop, it would be extremely expensive.
Just to get the parchment you'd have to slaughter a herd of ovines, then you'd have to process it, then you'd have to pay a skilled professional or more for months of work to draw and write.
So I think the profit motive is more likely, and given we know of a ton of scams like this from this period, it seems the most plausible.
But I'll be happy to be proven wrong if someone finds more info in the future.