Here's the announcement I saw, with a link to more information.
So, news is now out that there's a new book of J.R.R.T. material due out next year (May 27th 2021). Edited by Tolkien linguist Carl Hostett...
sacnoths.blogspot.com
The first ever publication of J. R. R. Tolkien’s final writings on Middle-earth, covering a wide-range of subjects, and the perfect next read for those who have enjoyed
Unfinished Tales and the
History of Middle-earth series and are hungry for more.
The Nature of Middle-earth will comprise numerous late (c. 1959-73) and previously unpublished writings by J.R.R. Tolkien on the “nature” of Middle-earth, in both chief senses of that word: both metaphysical and natural/historical.
For Tolkien fans, readers, and scholars interested in learning more about Tolkien’s own views on Middle-earth. It will appeal in particular to those readers who enjoyed
Unfinished Tales, and some of the later volumes of the
History of Middle-earth. Indeed, many of the texts to be included are closely associated with materials published in those places, and were sent to Hostetter, specifically, in photocopy by Christopher Tolkien for potential publication.
Much as
Unfinished Tales forms an unofficial thirteenth volume of the
History of Middle-earth, this new book will sit very nicely alongside as an unofficial 14th volume. Of particular note, given the impending Amazon series, are several texts detailing the lands, flora, and fauna of Númenor, and the lives of Númenóreans.