But yeah, that's annoying.
https://www.tandfonline.com/doi/full/10.1080/01611194.2022.2...
It could have been broken long ago if anyone had thought it was interesting. So it's less like deciphering the Voynich Manuscript and more like finding a cache of letters at a yard sale.
"The letters reveal Mary’s distrust of Walsingham and Sir Robert Dudley, Earl of Leicester, who was a favourite of Elizabeth’s. In the letters, many of which were sent to the French ambassador to England, Michel de Castelnau de Mauvissiere, Mary complained about her poor health, the conditions of her captivity, and spoke about her efforts to negotiate with Elizabeth for her release. The letters document her attempts to win over some of Elizabeth’s officials with presents. Mary also expresses her distress about her son, referred to as “mon fils” or my son, later King James VI of Scotland and James I of England, who was taken away from her at the age of one."
Also mentioned,
"... The authors noted that seven of the eight newly decoded letters turned out to have plaintext copies preserved in British archives, adding, "It would seem that the leak from the embassy was quite effective and comprehensive" ..."
, as there were some spies at the time in the French embassy that were leaking the decoded texts.
Btw, there's doi link at the end of the ars article.