J. K. Rowling has mentioned it on X/Twitter in the last day or so. She's been on Sark for research purposes. She says a few chapters will be set there. New title is The Hallmarked Man. No publication date yet, but speculation is if she's nearly finished the manuscript it could be out before Christmas this year.
https://www.therowlinglibrary.com/2024/03/15/j-k-rowling-reveals-title-of-strike-8-the-hallmarked-man/
I think I read a book set on Sark when I was a child. I've always wanted to visit it. Maybe this will be the spur I need.