Man, I went down that rabbit hole last month. There's no complete free audiobook from what I could find, at least not legally. The author's official site and places like Audible have it, but it's paid or requires a credit. I did stumble across a few podcast platforms that had the first handful of chapters narrated by fans—the quality was hit or miss, one narrator made every character sound vaguely bored. It vanished after chapter 7 though, probably got a copyright strike.
What I ended up doing was using the free trial on a major audiobook service. You get one free title, so I grabbed 'Saving Nora' with that. Finished it in a week and cancelled before getting charged. Felt a bit sneaky, but it worked. For a full free listen, you're likely out of luck unless your library offers it through an app like Libby, but mine didn't have it.