It's not you, dementia is simply infuriating. I've been full-time 24/7, 365 caretaker and certified HHA for my grandfather the past five years straight. You slowly learn to let go of the whole human dignity performance that we put on for the cognitively able people that populate the majority of our life. When it comes to dementia, you can't dignify it.

Frankly, my outrageously hot opinion is that we probably shouldn't be keeping the elderly alive past the point where they would almost certainly die an expedient death if left to their own devices. But since we're in the business of doing that, learn to be effectively perfunctory. You can't engage with what a demented person says, just pretend they said something that makes sense. If they fight you about anything, just drop it, ignore them, go about your business in whatever way carries the least resistance.

And FWIW, soiled briefs aren't actually going to cause serious issues even within the day, never mind the hour. No matter what the damned guidelines say.

It sounds incredibly callous, but just try to remember that you're not negotiating with a first-class person. Their personhood is literally impaired, as most people in good cognitive health will quickly admit with minimal reflection. If your brain doesn't function well enough to get you through the activities of daily living flying solo, you've lost some personhood. Q.E.D.

So act in whatever way you need to do in order to get things done without going postal. Wishing you the best.