If this is true then this news is sweet

I've seen something about a new book on Instagram, too

I also heard it and they say it has Tolkien's signature but I'm a bit suspicious about it because the more a writer is successful the more books appears suddenly 😒

Nature of Middle-Earth is indeed a new book by Tolkien. It is going to be similar to Unfinished Tales. More of his stories and writings compiled together. One website said its essentially an unofficial addition to The History of Middle Earth series.