It is literally reported here in the same story. Just need to actually read to the end: "Apart from HIghlander, Microsoft also tested an underwater data center

It is literally reported here in the same story. Just need to actually read to the end: "Apart from HIghlander, Microsoft also tested an underwater data center way back in 2015 as part of its Project Natick off the Pacific coast and then two-year tests off the coast of Orkney, Scotland, in 2020. While the company touted multiple benefits of the approach, it has not proceeded with newer projects in this direction since."