The compose key feels mandatory for anyone who wants to type their native langauge on an US-english layout. The combination[0] is "Compose--." though: –

[0]: https://en.wikipedia.org/wiki/Compose_key#Common_compose_com...

“Compose--.” produces an en dash, not an em dash. An em dash is produced by “Compose---”.

Source:

  grep -e DASH /usr/share/X11/locale/*/Compose

As it should be. I wish this convention were present across more software, “-“ “- -“ and “- - -“ should be the UI norm for entering proper dashes in text input controls.

Most software handles this fine if you configure your compositor to use a compose key.

Whoops, yep that's the one