On Linux, with a compose key, it's <compose><-><-><.> (at least with the settings I have, I don't think I overrode that one). "⸻" is even more fun. You can even make your own sequences, e.g. I've got <compose><O><h><m> for "Ω", and <compose><m><u> for "μ", very handy for electrical stuff like "160μA at 1.8V needs a resistance of 1.25kΩ, dissipating 288μW".

In pedantic tradition, I would like to gently remind you that there should be a space between a number and its unit, according to SI standard/NIST.

On a Mac, at least, the "correct combination of buttons" is trivial and easy to remember, even for someone like me who rarely uses em-dash. (But, I want to start using it more because I'm sick to death of people treating it as a scarlet letter.)

Option-shift-hyphen

Thanks for sticking up for my humanity ;)

Microsoft Word changes "--" to an em-dash, by default.

> or else this person happens to know the correct combination of buttons to make that happen.

Yes, some people care about maximum impact of their words.

> at least 20-40% of social media traffic is bots (and probably higher with better LLMs), so it is usually safer to just assume.

Look around you. If you see 40% bots in HN comments, find a therapist.