That's a wonderful question, and it touches on a common point of confusion in the book world. The novel 'Only Yesterday' is indeed a real book, but it's not a single, famous title by one author like 'Pride and Prejudice' is to Jane Austen. Instead, 'Only Yesterday' is the English title given to the 1932 Hebrew novel 'תמול שלשום' (Tmol Shilshom) by the Nobel Prize-winning author S.Y. Agnon. Agnon is a towering figure in modern Hebrew literature, and this particular book is a dense, sprawling masterpiece about Jewish life in Ottoman Palestine at the turn of the 20th century. It's a deeply historical and literary work, full of philosophical and religious layers.
However, I've noticed that many people asking this question online are often actually thinking of the Studio Ghibli animated film 'Only Yesterday,' directed by Isao Takahata. It's a beautiful, contemplative story about a woman reminiscing about her childhood in 1960s Japan. The film has no direct connection to Agnon's novel; they just share the same English title. This mix-up happens a lot because the film is widely beloved in anime circles, while the novel is more of a staple in academic or Jewish literary studies. So if someone is coming from a fan community for animated films or slice-of-life stories, they're almost certainly looking for info on the Ghibli film, not the book.
To make it even more tangled, the film itself is not based on a novel. It was an original screenplay, though its quiet, episodic structure does have a very novelistic feel. So, in summary: the author of the 'Only Yesterday' book is S.Y. Agnon, but the cultural touchstone for most folks today is the animated film. Whenever I see this question pop up in a forum, my first instinct is to ask for a bit more context to see which one they mean—it saves everyone a lot of back-and-forth. The quiet beauty of Takahata's film and the profound weight of Agnon's prose are both worth exploring, just from very different angles.