Father with mild to mid dementia is waking up at night. Any tips?

My dad lives with me so I'm familiar with his daily cycles. Dad has mild dementia associated with Parkinson's. He does exactly as you describe, probably for similar reasons. He also has acid reflux and frequently has GERD at night. I don't have a silver bullet but here are some things that I've tried.

In this past, Dad might have multiple beverages with his dinner. I prepare most of his meals, so I can calibrate this. I offer him a small glass of whatever he wants, and I never offer him a refill or second beverage with dinner. Less in means less out.

There are foods that are natural triggers for GERD and I avoid those like the plague. I don't even keep them in the house, and if he asks for those (usually pasta), I "forget" to buy them at the store.

In the more recent past, he might have a couple of beers with dinner, and I gently steer him away from that. Alcohol disrupts REM sleep.

Given his own devices, he would go to bed at 6:00-6:30 and then be restless through the wee hours of the morning. I am not a night owl either, but I try to keep him up an hour or two little later so he's actually tired when he goes to bed. I'll propose we put on a movie he likes while we eat dinner (yes, he likes to watch TV with dinner - not sorry). He'll get engaged in the show and want to see it to finish, so he goes to bed and is actually tired.

Dad has restless leg syndrome, which is comorbid with parkinsons. I found that caffeine was one of his triggers, so we slowly weaned him off coffee and other caffeinated beverages. Now he has a thermos of hot cocoa every morning instead of coffee, and I don't keep much soda in the house. The restless legs never totally went away, but it's gotten a lot better.