I switched from Due to the stock Calendar app on iOS over the weekend.
Due is very good at nagging me until something gets done, but it unfortunately doesn't understand what an upcoming event is, and it has no concept of a time span, nor a way to get a proper overview. Also, the macOS version of it is quite sloppily executed.
Unfortunately, the alerts in Calendar don't work any better for me than they did the last time. Sometimes, they don't work. At other times, I miss out on them.