Suggest me a sci-fi book about loneliness

I've been craving a very specific type of book, a novel that's character driven set in a post apocalyptic futuristic sci-fi world where our protagonist is the only human left alive/on Earth. They'll be going through a self discovery or acceptance journey about their own loneliness as they journey through this vegetation overgrown world with sprawling white skyscrapers and futuristic tech, most of it barely operating, if at all. Or even a premise where they have a predetermined timer that will solidify their death like a disease, lack of food or fuel in a world dependent on scavenging and traveling, they'll have to come to terms with their inevitable death where they'll be surrounded by no one, something like the first 3 minutes of this video (view comments).