When I woke my computer from "Sleep mode" on the morning of 14 Jan 2023 The Event Calendar on the right pane still showed the date as 13 Jan 2023 As illustrated in the first screen shot, there are even 2× "Today" entries, one for the 13th, and one for the 14th. When bringing up a new Event, by tapping the new Event button button, even the dates defaulted to the 13th, and not to the current day, the 14th. Tapping the "Today" button in the header of the Calendar Event pane, did force the pane to refresh, and update itself. Subsequently, a "New Event" was dated to "today" by default. This has happened on previous versions of Thunderbird, I just happened to document it this time. Most days (99% of the time), my computer is shutdown, so on restart, when Thunderbird launches, the Calendar Event pane syncs with the current date by default.