Found out unexpected keyboard on Android can do it. Desktop.. no idea

On stock gboard holding dash in the symbols keyboard will let you type emdash. There are a lot of secondary symbols accessed that way. —

Usually you just type two hyphens together and the editor converts it to an em-dash. For this of us old enough to remember using typewriters, that is, typographically, how you type an em-dash on a typewriter.

— til emdash — hold my finger down for secondaries :—)