This summary is not the rule. The rule text controls.
When a jury is deciding a case with more than one defendant, they don't all have to agree on every person at the same time. If the jury reaches a decision about one defendant but is still stuck on another, they can turn in a verdict for the defendant they agree on. The case continues for the other defendant.
The same idea applies when one defendant faces several charges. If the jury agrees on some charges but not others, they turn in verdicts for the charges they agree on. They don't have to reach a decision on every single charge before submitting anything to the court.
If the jury truly cannot agree on a particular defendant or a particular charge, the judge can declare a mistrial just for that part of the case. This means that specific charge or defendant may need to be tried again later, but it doesn't undo the verdicts the jury already reached on the other parts. This system prevents a total do-over of the whole case just because the jury got stuck on one piece of it.