The open access paper is:

George Lasry, Norbert Biermann & Satoshi Tomokiyo (2023)
Deciphering Mary Stuart’s lost letters from 1578-1584, Cryptologia,
DOI: 10.1080/01611194.2022.2160677
[www.tandfonline.com]

Another article is:

3 amateur codebreakers set out to decrypt old letters.
They uncovered royal history, NPR, February 10, 2023
[www.npr.org]

Yours,

Paul H.

"The past is never dead. It's not even past."
William Faulkner, Act 1, Scene III, Requiem for a Nun (1951)