Luigi Mangione

This is just a motion. Judge will decide it's validity and the remedy. It might end up with the evidence excluded, but it might be that the prosecution just has to provide a different/stronger justification, or even be a nothing burger if the judge is unconvinced by the arguments in the motion.

I agree with your analysis if the judge does exclude backpack and contents as evidence.

Anything other than exclusion will be grounds for appeal, later, too.