On iOS it is possible to copy contacts (from the Apple contacts app), via a shortcut “copy to all devices” and paste them into Agenda. On MacOS, you can just drag them in.
So then, through “preview” in the sub-menu for tags, people and, in this case “contacts”, you can make a call, message or email right from within iOS Agenda.
Just one thing: preview on iOS doesn’t always work. It does most of the time but not always. Any idea why?
Ps: if I write a phonenumber in a note, it sometimes turns out “clickable” (i.e. callable) and sometimes as just another number.