Speedboat by Renata Adler.
Jen Fain is, we gather, a journalist, working primarily in New York. I say "we gather" because there's nothing as gauche or jejune as a standard orthodox narrative here, my goodness no.
What we have to do here is gather information as we go along by sifting through a series of reflections and anecdotes presented as short paragraphs and working out whether they relate to Jen's life, stories that she has encountered in the course of her journalistic activities, or just random musings on topics of interest.
So we gather that Jen is youngish, probably twentysomething, a journalist for some New York tabloid, living in the 1970s, going to far-flung and occasionally dangerous places for work, hanging out with other journalists, having fairly desultory relationships with men, usually also connected to journalism or politics in some way, including her current partner Jim and possibly a guy called Aldo in the past, though the chronology of any of the fragments that describe these things is hard to establish with any certainty. So Jen works through various jobs at the paper - film critic, gossip columnist - but not necessarily in the order portrayed here. She hangs out with her friends, also mostly from the New York journo/politico inner circle, and observes some of them marry, divorce, have kids, die, all the usual stuff. She dabbles with various leisure pursuits - shooting, tennis, flying lessons - without a firm commitment to any of them.
Eventually Jen discovers that she is pregnant with Jim's child and has some pivotal life decisions to make: keep the baby? tell Jim about it? The book ends without these key questions being resolved.
Speedboat was first published in 1976 - Renata Adler was a journalist of some note by that time (as always, write about what you know) and the book won some awards on its original publication but was then out of print for some years before being revived; my W&N Essentials edition dates from around 2021.
I recall seeing Speedboat being mentioned in the reviews of Jenny Offill's Dept. Of Speculation, a book structured in a broadly similar way. Pretty clearly the later book was explicitly influenced by the earlier one, though I think you could argue the later book has a slightly stronger narrative thread running though it, especially in the second half, which (just to stretch the metaphor a bit further) gives the reader something to hang onto, especially if you find yourself reading the book in lots of short segments (last thing at night, on the train, in kids' swimming lessons) as most busy normal people who are not paid book reviewers or minor royalty with no need to earn a living will find themselves doing, and having to re-orient yourself within the book's structure every time you pick it up.
The authorial voice, though not the structure particularly, is very reminiscent of Joan Didion: there's the journalism setting, of course, but a general sense of the narrator being cool and fabulous and self-possessed even in rough and dangerous country, and an air of slightly ironic detachment and amusement at the antics of the people who occupy most of the narrative. As with the Rachel Cusk novels we end up learning most of what we know (or think we know) about the narrator through other people.
It comes down to a question of taste in the end: I like to think I'm quite open to formal experimentation in novels, and the fragments - considered as individual pieces of writing - are all beautifully written and slyly observed, but the coolness and emotional detachment of the whole thing made it - while easy to admire - hard to engage with. I suppose it's a similar thing to my reaction to David Bowie's work (substitute "novels" for "music", obviously):
I suppose the way I would put it is: my preference is for people to totally be "in" their music, rather than standing an ironic distance away from it and pointing at it.
I think if you want an example of this type of work then Speedboat is probably a better book than Dept. Of Speculation, though there's plenty to admire in both, and they are both pretty short, though not the type of books to keep you up all night breathlessly turning the pages to find out what happens next. That's OK, though.