[cosmic_cheese]

It’s a per-app setting that sometimes needs to be set in the text field’s context menu. There’s also a few apps that just don’t integrate with the macOS text system.

[wk_end]

Well, I see no way to set it in Chrome. A good reason to be a little suspicious of Reddit or HN posts with em-dashes IMO.

[eclipticplane]

It does on Safari (Mac and iOS) by default on Reddit.

[latexr]

Probably under Edit → Substitutions. That’s where it usually is in apps.