> Long press on - on both iOS and android (Gboard)

Depending on the text area you are typing into, if you type two hyphens/minuses right after each other (no spaces), Apple systems often translate them to an em-dash (kind of mimicking (La)TeX).

(If you don't want the em-dash, hit <cmd-z> with macOS to undo that auto-conversion.)

did not know that

Y'all on Android should be using Unexpected Keyboard, where it's Compose - - -.