A more recent book worth checking out regarding modern pessimism is Szymczyk's Atlantis & Its Fate In The Postdiluvian World, slightly philosophical and extremely pessimistic at times, bordering on science-fiction at others, but overall a highly entertaining read with some interesting comparisons of Kodiak Island around 10,000 BC with descriptions of Atlantis in Plato's Timaeus and Critias. He also mentions Schopenhauer quite a few times, which is why I'm mentioning it (disclaimer: I know the author and have been championing this book so I might be a bit biased, however, the book is free on Kindle right now so this is not a commercial endorsement).

I also recommend reading The Last Hour of Gann by R Lee Smith. Looks like shitty alien erotica, but is something like 800ish pages of debate about what it means to be human. One of the most honest takes that I’ve ever read. Is like seven different genres.

It’s not precisely pessimism, but dances around the topic with the plot. (I’ve read Ligotti, but I think R Lee Smith conveys stuff in a way that is really clever. She doesn’t have answers for anyone, basically—I thought Ligotti was heavy handed.)