I'm starting to wonder if this is a sign of approaching death. He still enjoys a few activities like listening to music, going for car rides, having his physical therapy sessions twice a week. But he won't eat anything except ice cream, chocolate pudding, etc.
Oh and by the way...the lady who only ate ice-cream and cashews lived to be 103.
As we age, we lose our sense of taste: salt, sour, bitter, umami (savory) and sweet. Sweet is the last to go. He probably can't taste much of anything else. In old age, there becomes fewer and fewer things we can get enjoyment from and eating is still one of them.