This summary is not the rule. The rule text controls.
If someone thinks a defendant isn't mentally able to understand the charges against them or help with their own defense, that concern can be brought up at any point during the case. It doesn't matter who raises it. The defense lawyer, the prosecutor, or even the judge can bring this question forward.
Once someone raises this question, the case has to stop moving forward. The court can still file charges to start the case, but nothing else can happen after that. No hearings, no trial, no other steps can move ahead until the court decides whether the defendant is mentally capable of understanding the proceedings and assisting in their defense.
This rule protects defendants from being tried or punished when they can't understand what's happening to them or can't properly help their lawyer. The case stays on hold until a judge determines the defendant is capable of moving forward. This makes sure the legal process is fair and that no one is judged while they lack the mental ability to take part in their own defense.