When the current day's cell has overflowing events, the cell should auto-update throughout the day to prioritize future events based on current hour, move past events to the overflow
In the weekview's timetable, we have a Marcus Bains line (the blue line in the screenshot below) that shows the current time throughout the day. In this screenshot below, you can see there is already a gray-colored event in my calendar that is in the past compared to the line:
...whereas in month view, there is not enough space to show all events at once in that day's cell, so they overflow (into the "+2" button):
In the case where a day has overflow (too many events), as the current day progresses, GNOME Calendar's month view should move the day's "past events" to the overflow widget (the +2 in the screenshot above), allowing to display more relevant events. So, in the example screenshots above where the time is currently 13h55, it should take out the gray "arroser" event (that was scheduled for 12:00 to 13:00) in order to have space to show the blue "photo-d" (15:30) event that comes after the purple "interview" (14:30) event. The gray "arroser" past event could be put into the overflow instead of the blue one.
Of course if someone deletes/moves events within the day, then this calculation needs to be redone. I also suppose that once the day is over (i.e. the time moves past midnight) it could just reset that day's cell/oveflow, to showing the events from the start as it currently does (just to avoid potential bugs there).
Maybe we can be extra-smart about it, and evaluate how much time there is between now and the next "hidden by overflow" future event, and do this only if the next event is more than 30 minutes into the future, and if the previous event ended more than 30 minutes ago (to avoid the case where you are a few minutes late to an event that you forgot about; realistically, 30 minutes should be plenty).
Otherwise, if that's too complicated, we can just look at the exact times; it'll still be much better than the current situation already.