Literally everything about euthanizing someone who resists at present, but consented in the past is hard. We shouldn’t pretend anything about this is straightforward. These are agonizing decisions, and we should acknowledge them as such
If my advance directive says "please give me MAiD when my dementia gets to the level that I'm a burden on my loved ones", them the answer is you give me MAiD, not respond to my delirious protests.
If you don't know how to "interrogate delirium or confusion", you shouldn't be a doctor.
There is NOTHING HARD about this scenario, except if you don't understand how brains work.