From Nerdist:
Dark Horse Announces Buckaroo Banzai Sequel Novel
The book is now in pre-order status at Amazon, and will come out August 10, 2021.
Apologies if this info's been already posted.
The work of the film’s original screenwriter and novelist Earl Mac Rauch, The Adventures of Buckaroo Banzai Against the World Crime League, et al: A Compendium of Evil will find the world renowned physicist, neurosurgeon, test pilot, and rock star, Dr. Buckaroo Banzai, as he finally goes head-to-head with the evil organization the end of the first movie promised.
The official synopsis is thus:
Still mourning the losses of his beloved Penny Priddy and his surrogate father Professor Hikita, Buckaroo Banzai must also contend with the constant threat of attack from his immortal nemesis Hanoi Xan, ruthless leader of the World Crime League. To make matters worse, Planet 10 warrior queen John Emdall has sent her Lectroid legions against Earth with a brutal ultimatum. Or is her true target Buckaroo Banzai? As the apocalyptic threats continue to mount, only Buckaroo and his Hong Kong Cavaliers stand in the way of global destruction—or in the words of one of the movie’s iconic lines: “Laugh-a while you can, monkey boy!”
Dark Horse Announces Buckaroo Banzai Sequel Novel
The book is now in pre-order status at Amazon, and will come out August 10, 2021.

Apologies if this info's been already posted.