Hey Guys!
I finally found a way to make this “global hotkey” happen! A not-so-neat accomplishment, but it’s very useful while we wait for an “official” quick entry global hotkey in Agenda, and maybe it can help others too.
I used macOS Automator to do this workflow, even though there are people who don’t like it. If you know a better way to do it, I’m open for suggestions! 
I’m guessing that people who ended up here in this thread might know some features I’m about to describe. But, if you don’t, feel free to ask. One more thing: my macOS is in Portuguese, so I don’t know how exactly the English commands are presented… Be nice, ok?!
Anyway… follow these steps. It’s pretty easy, but it won’t cover what I wanted, which was creating a note in a specific project.
So I included two more steps in the workflow:
- Dragged and dropped the “Get Specified URL” (which is in Actions>Library>Internet) and added the x-callback-url that I wanted (you can find its documentation in this community), which looks like this:
agenda://x-callback-url/create-note?project-title=Notas&title=Ideia&on-the-agenda=false&date=today
(if you’re like me, here’s a brief explanation: it tells Agenda to create a note, in the project previously named as “Notas”, with the title “Ideia”, and as I didn’t want it to be “On the Agenda”, I put it as “false”, but with the date “Today”); - Then, added a last action called “Display Webpages”, otherwise it won’t work (believe me, I tried!).
Afterwards, I saved it as “Thoughts to Agenda” and did what is described in the link placed above (assigning a Keyboard Shortcut; mine is Shift+Cmd+I, for “Idea”).
And Voilà! That’s it! It doesn’t matter where I am in my computer, I simply hit this shortcut and a new note comes to the front, where I can write what’s in my head.
I hope you guys like it!
Best regards from Brazil!