What I did: Tried to create a link from one note to another.
What happened: Couldn’t; greyed out all link options. But then later I can???
What I expected: Just to be able to link, any time.
Things that might be helpful to know (Agenda version, OS and model, etc): Latest everything (No beta, on Mac, sync with iCloud). You might want to put version info in the About Agenda splash.
Are you sure you were editing a note and the cursor was blinking?
You might want to put version info in the About Agenda splash.
It does already.
Ahh, you have to be editing the content of a note to add a link?
I assumed links were something entireley different. I assumed I was creating a link between notes, but in fact I’m adding a link to the current line of a note only.
I assumed I could link the note itself; selecting it (without a blinking cursor) or selecting the title, to another note.
Correct, you need to be in a note itself, it becomes an inserted URL.
Yep; sorry I missed that. I even glanced at it thinking it would be there. It was, just a bit tiny for these old eyes. 
