> So do you always put in the ALT+<code> incantation to get an emdash or copy&paste?

There’s no incantation. On macOS it’s either ⌥- (option+hyphen) or ⇧⌥- (shift+option+hyphen) depending on keyboard layout. It’s no more effort than using ⇧ for an uppercase letter. On iOS I long-press the hyphen key. I do the same for the correct apostrophe (’). These are so ingrained in my muscle memory I can’t even tell you the exact keys I press without looking at the keyboard. For quotes I have an Alfred snippet which replaces "" with “” and places the cursor between them.

But here’s the thing: you don’t even have to do that because Apple operating systems do it for you by default. Type -- and it converts to —; type ' in the middle of a word and it replaces it with ’; quotes it also adds the correct start and end ones depending on where you type them.

The reason I type these myself instead of using the native system methods is that those work a bit too well. Sometimes I need to type code in non-code apps (such as in a textarea in a browser) and don’t want the replacements to happen.

> I feel the emdash is a tell because you have to go out of your way to use it on a computer keyboard.

You do not. Again, on Apple operating systems these are trivial and on by default.

> Something anyone other than the most dedicated punctuation geeks won't do for a random message on the internet.

Even if that were true—which, as per above, it’s not, you don't have to be that dedicated to type two hyphens in a row—it makes no sense to conflate those who care enough about their writing to use correct punctuation and those who don’t even care enough to type the words themselves. They stand at opposite ends of the spectrum.

Again, using em-dashes as one signal is fine; using it as the principal or sole signal is not.

On Linux, I configured my Caps Lock key to function as a compose key, and then use my ~/.XCompose file to make it easier.

I also set things up such that hitting Caps Lock twice in a row sends an Escape character, which makes using Vim a tiny bit nicer.

On Windows, I use autohotkey and have a bunch of keyboard shortcuts for producing characters that I use fairly often but are difficult to type.

My keyboard has no keypad so I’m not sure there’s another way.

You type -- and it gets auto converted.

no I use -- and ---. not all of us use Microsoft word for serious writing.