They just run a grinder along each platter. Enough to make recovery extremely difficult.
Another place had a shredder that you could toss whole phone books and even electronic components into. They would toss drives into it and what came out was no bigger than maybe 2-3”. But that was a heavy duty machine that I’m sure cost lots of $.
Back in the days of floppies a good way to kill them was put them in the lunch room toaster oven. I was told even the microwave, though I never tested that.