Ok? but the clue is that the key is the "32 Proquiritations" immediately before the numbers. Not that it is a book cipher. Both Jan and Helmut misses that. Jan assumes that the keys are the "names of the ancestors", while Helmut assumes that the first row are page numbers and the second row are word numbers. With hindsight both appear to be incorrect, thus they missed the hint.
> It appears that is not true.
Strong words. I don't think your comment supports them.
Let's look at each part of the quote you claim is not true.
"Various people attempted to decipher it". Your link support this, doesn't go against it.
"but it seems they were missing one crucial hint." the link you provide doesn't show anyone getting the right hint. Yes they were groping in the right direction, but they didn't get that the "32 Proquiritations" is the key itself.
"They tried methods like frequency analysis, substitution, and homophonic substitution, and none of these approaches worked." I don't know if people tried these methods. The sentence doesn't claim these are the only method people tried. That would be obviously unsupportable. So as long as there is someone for each of these methods who tried them the sentence is true.
"That’s because they missed one easy clue." It is obviously impossible to prove that everyone missed this clue. Maybe someone during all those years got the hint, solved the riddle, chuckled and never wrote about his experience. Perfectly possible and we won't ever know. What is certainty that the people on the link you provided misses the hint. But you also haven't shown that those people "got the clue".
So which part do you feel is "not true"? Because they each seems to be holding up.