If you can muster the energy to play with him before bedtime, like get him jumping and climbing and chasing until he's nice and tired, it might help him settle down and sleep through the night. He's probably more lonely than hungry, but a little kibble after playtime might also help make him sleepy.

Sorry to hear about your cat. We lost our old boy about two years ago. He was about that age. He was the best lap cat.

He might need some time to adjust to the change in routine? It's tough to say. I had one cat about your cat's age who was very social and routine oriented. After his wild adjustment period, he settled in, and he would sleep all night. I hope consistency is all you need, too, but my cat might've been a weirdo.

Another cat figured out nighttime was when humans sleep only after closing her into the other half of the house when she wouldn't let us rest.

When our first cat died, number two also acted very weird. He was searching his buddy for weeks without stopping. After a while we brought him company, since his mental Health seemed to be on a decline. Having a new kitten helped him out of this situation and now he has a new best friend 😁

Still miss our first one 🥹

Sorry to hear about your cat. That shit is rough.

That aside, I think the only solution is more cats!

Something you could try is calming treats before bedtime. My friends cat is starting to suffer early signs of dementia and the “composure” treats have been helping him make it through the night. Also, there are more stimulating cat feeders, like this one. You basically start by feeding them in the normal place, and then progressively move the little feeders further and further away from each other until you can hide them, stimulating their hunting instincts, satisfying them with mental challenges, and ultimately making them more content. The company itself claims it’s meant to help your cat sleep through the night.

Some cats get lonely and it's not about play, but knowing they have options. When I had a similar situation, my 3 year old cat pulled out her belly fur from stress, so I got her a new friend. Over grooming immediately stopped. It took several months for them to be friends, but my first cat was MUCH happier having another cat.