Is it normal for a 92 year old to sleep 22 hours a day?

The real question is, is it normal for him? If the amount of time he spends asleep has gradually increased, then yes, it wouldn't be unusual with advancing dementia. But if he's normally been alert for much longer periods during the day and this is a comparatively sudden change, then you should report it to his PCP or medical team and ask their advice.

My 92 year old dad has Alzheimer's and sleeps almost 20 or 21 hours per day.