alt Hacker News> on Mac, for example, it’s simply Option + Shift + Hyphen
And on Windows it's Alt + 0151 on the numeric keypad, which means you a) must have a numeric keypad and remember the number, or b) must use the emoji search. And on Linux it's weird too.
Em dashes are therefore Mac user garbage. The correct replacement is --
MS-Word will replace " - " inside a paragraph with an em dash, fwiw. I don't know for sure about other word processors, I don't use them much tbf.