https://luxurylaunches.com/transport/the-abandoned-alfa-nero-superyacht-is-burning-2000-of-diesel-everyday-to-run-its-air-conditioning-just-so-that-mold-and-sea-water-do-not-ruin-its-opulent-interiors-and-expensive-paintings.php
https://luxurylaunches.com/transport/the-abandoned-alfa-nero-superyacht-is-burning-2000-of-diesel-everyday-to-run-its-air-conditioning-just-so-that-mold-and-sea-water-do-not-ruin-its-opulent-interiors-and-expensive-paintings.php
It's probably a steel hull. The easiest way to sink it would probably be to break some through-hull connections below the waterline. Not much you can do from outside other than perhaps plugging the bilge pump's output.
Or you could wait till a big storm and cut the docklines.