iOS 14 Widget auto-refresh every day
Actually, it seems to be I overlooked it, the widget actually refreshes, it was me, who didn't refresh the data itself. (I'm using UserDefaults to share data between my app and the widget, and even though the widget refreshed properly, as the data in UserDefaults was not updated, the same was shown over and over again.)
This should save you a few lines:
let nextUpdate = Calendar.autoupdatingCurrent.date(byAdding: .day, value: 1, to: Calendar.autoupdatingCurrent.startOfDay(for: Date()))!