It closed down indeed. But I'll leave this Note open, becuase something new will be build here soon-ish. The last update on the city's website is from december 2022, but according to the time table published there construction should start roughly in summer 2024.

https://www.kiel.de/de/kiel_zukunft/kiel_plant_baut/britischer_yacht_club/index.php

Changed name to old_name:
https://www.openstreetmap.org/changeset/150483968