Have you tried setting up the compose key?

It seems like it can do the em dash and any other special characters you want:

https://tstarling.com/stuff/ComposeKeys.html

A compose key is a great option. You can also use something like Kanata to make a custom layout that's the same as your normal one, but with extra characters on the AltGr layer.

While not as powerful (i just miss Autohotkey) xdotool is a good alternative for ahk. Create your script with it and use a hotkey to run it. Like:

xdotool type "é"

I use a tool called Espanso for this type of thing. It's available on Linux, Windows and MacOS. It's a text expander app that allows you to enter long passages with a simple keystroke, but can also be used to enter special characters. One minus is that the configuration is done in text files using YAML, but it's not at all difficult, and the documentation is very good.