I have read the manual, searched forums, seen Divkids video but I still don’t understand how the Four voice polyphony in 2 hp Pluck works.
Very glad if someone could explain.

I've not read the manual nor do I own it, but I suspect it works similarly to rings - pluck and/or change note quickly and the last 4 notes will overlap - giving you 4 notes playing at once - 4 note-polyphony

yep, each 'String' on a guitar (for instance) keeps resonating after being plucked, so one String can be played at a time but the decay of that string rings on into the others.

The 2hp Bell works in a similar way but has 6 voice polyphony, though each bell-strike can have quite a bit of a different resonance to the last, kinda de-tuned.