The thing with em dashes is that most keyboards I’m aware of don’t have dedicated em dash keys, and most text input on the web won’t parse a double hyphen into an em dash the way word processors do. Ironically, Lemmy’s markdown parser does exactly that. – —. I suspect it’s based on or connected with Pandoc’s markdown parser, since how you enter collapsable spoiler blocks is identical to Pandoc’s div block notation

::: spoiler some text
Hello world
:::