If you have the compose key enabled it's trivial to write all sorts of things. Em dash is compose (right alt for me) ---

En dash is compose --.

You can type other fun things like section symbol (compose So) and fractions like ⅐ with compose 17, degree symbol (compose oo) etc.

https://itsfoss.com/compose-key-gnome-linux/

On phones you merely long press hyphen to get the longer dash options.