Early this morning at about 00:40, the van alarm went off.
The blockmap records last four events in groups 20 (the last) - 23 (the earliest).
The recorded time was 00:35 and the alarm source was code
12 = Alarm horn. Sorry but I do not have any more details what exactly that means. Wiring issue or water ingress in alarm horn circuitry?
Perhaps the following would need to be rectified?
Side door unlocked but not open.
Tailgate unlocked but not open.
The earlier codes were (possibly) more self-explanatory
21 = Central locking alarm delay driver's side
5 = Engine hood
10 = Interior monitoring
The alarm sounder battery report status OK.
Battery is OK, but nothing brilliant.
So the blockmaps were recorded ignition OFF?
During the recording voltage was only at 11.2 Volts

Also the blockmap shows remaining battery capacity was 0 Ah, so obviously would need immediate charging.
Possibly a more serious indication of battery health is battery's internal resistance (normalised) reading (for comparison my battery readings, and readings 8 years ago ). My impression is that the internal resistance would be a fairly reliable measure for battery's long term state of health - on mine it has been steadily deteriorated over the years.
Perhaps you could try to charge the battery - just to see if the number get any better.