This is not about system autocomplete, it's about an autocomplete internal to Calendar (autocompletion of the name of the event when you create one) – and is there any way to turn it off.
I have many hundreds of events in ical as I've been using it for about the past five years.
Problem is whenever I create a new event, then start typing in the event name field, as I work out what I want to call the event (or reminder), a giant list of similar past events that I've entered pops up and is annoyingly distracting. I'm simply not interested in those past events anymore and I don't want to know about them. I use ical as a reminders system for tasks, i.e. as a todo list as well as calendar. I find that better than using a separate task app in addition.
I'd love to find a way to turn these suggestions off, without having to delete all past events from my calendar history (which it looks like I might have to resort to).
Haven't found a way to do this but would be very grateful if someone knows how.
Best Answer
I've just done a clean install to Catalina and signed in to iCloud. Without any action on my part, I no longer get the autocomplete suggestions when making new events. But I did not intend to disable them. Maybe that's helpful to someone.