Update
Just after posting this I removed the 4 limit expecting it to only display each event once, but it now displays 22 of them, which I guess is the default “limit”.
Each day of a multi-day event is considered a separate event and is listed individually on the calendar and in the upcoming lists. This is historical behaviour that has been around for many years. So when you configured the widget to 4, it includes the upcoming 4 days in the list.
I see. That’s a bit strange though. Because while the event occupies multiple days and is in that sense “multiple” events, they all still originate from a single entry. I guess I just didn’t expect it to behave that way.
I don’t really see the use of displaying a multi-day event that way, that is, as if they were multiple single-day events.
The way I’d expect (and like it to work) would be to display the first day as upcoming, and once the event has started it would no longer be “upcoming”, instead you could potentially have it under “Ongoing Events” instead, which might display events where the starting time has passed, but not the end-time.
Maybe that’s what the “Today’s Events” widget does, but perhaps only for the current date, not the time.
It’s not a huge deal though, I guess I’ll just keep trying event plugins.