There is now an Amazon listing for an updated edition of the Official Guide to the TOEFL. According to the guide, the sixth edition of the guide will be published on July 10. This will be the first version of the guide to reflect the changes to the test that were introduced in August of 2019.
Update: The Amazon release date is now August 28
Update: Amazon listings for KINDLE versions of new books have been removed.
The listing does not indicate much about what else has changed in the book, but fortunately the audio and software content will be provided online instead of on a DVD. It is also mentioned that the book will still contain just four tests. Previously, updated editions of the book included a new practice test.