Can't decide if this is technically isekai or "trapped in the game".
Our main character is a tax accountant by day, otome gamer by night. She spends the last night of her life staying up a bit too late to romance a Prince, fighting off her rival Iris, the daughter of a Duke. On the last day of her life, she mostly gets hit by a van.
Of course, when she revives, she happens to find that she's now Iris, stuck in the game, in the scene in which the player character denounces her. The main character accuses Iris of bullying her, and the Prince has her banned from the court, leading (in-game), to her being sent to a nunnery.
Luckily, "our" Iris has both her own memories and those of the Iris character, which means she's able to wriggle her way out of the celibate life, and instead becomes the head of her new family's fiefdom. This covers a massive area, and has decent farmland, but struggles with social inequality and unsustainable wealth distribution. Good job she used to work in finance really.
Unfortunately, this is painfully bland. It's a relatively standard shoujo manga, with the classic artistic style, and a couple of helpful romantic leads added in for future use. Iris has a team of fanatically loyal retainers, most of whom she picked from the street where they were making a living as urchins. The character she's stepped into doesn't face any major difficulties, other than the financial problems which she's very well equipped to deal with.
That does make it feel like nothing actually happens in this first volume. There's the usual introductory "oh no, I'm in another world" and "well, I'd better make my life here livable" first couple of chapters (with a very quick adjustment), and then the rest of the book moves on to doing a census. Her team of investigators wander around the country, discovering everything wrong, and also realising she can invent chocolate.
That's more or less it. There are a few other bits and pieces intended to facilitate some character development later, but the entire book feels likes setup. It doesn't stand brilliantly as a complete work.
I think I'm getting increasingly burned out on these. There's only so many times you can read/watch someone try to upgrade a medieval world to modern, with the skills they unexpectedly possess. (I don't know about you, but I'd probably be dead in a week.) Might finally be time for me to rewatch Re:Zero. If you're absolutely desperate for something in this vein, it's servicable, but it's by no means worth digging out if you're not already a fan of the genre.