I haven't looked at the 7219 specs properly but I assume it pulls the digit select low as they are common cathode.
In that case you want say digit 1 and 2 to activate the same display. So the logic is
OP low if IP1 low OR IP2 low
That's an OR function with inversions on all pins, aka an AND function.
That's working on the digit being driven from a single 7219.
either one or the other MAX driving that line but never both
I can see no way of connecting both chips to a single display, they would never
be synchronised and segments would be lighting up all over the place.
2 MAX would drive the same common cathode at the same time. Do you think that makes no sense?
Yes I think that makes no sense
, because of the above reasoning.