But it's a careful what you wish for situation. I would REALLY like to go back to V11.4.9. This drive is now stressful and takes longer due to the car driving slowly.
My first drive experience with 12.3 was similar. Even on the 'assertive' setting, it wanted to drive painfully slowly on unmarked two-lane roads, like less than half the posted speed. (Much slower than any reasonable human.) It double-stopped at most stop signs; first stopping far short of the stop line (where it couldn't see cross traffic), then lurching ahead to the stop line, stopping again to get a better view, then finally proceeding.
In a five-mile drive in good conditions, I had to intervene several times to avoid getting honked at. The car often didn't accept the right of way, including once where it pulled up to a 4-way intersection and the opposing driver was turning left. I got to the intersection a couple seconds before the other driver, so had the right of way, but the car didn't take it, so it became a standoff. But as soon as the opposing car lost their patience and started the turn, my car lurched forward, and the other car had to step on their brakes and honk.
A minute later, the car surprisingly got into a clearly-marked left-turn-only lane when it needed to go straight. I've never seen it make this mistake at this intersection before, so this was a regression. A bit later, it needed to cross two lanes to a median, but it stayed frozen for about 45 seconds, even though there was absolutely no cross traffic, and no apparent reason why it didn't go. Eventually another car did go by, and after that FSD proceeded across to the median. A few blocks later, it reached an intersection where the lane became double-width (unmarked), to allow cars on the left to go straight and cars on the right to turn right. The car hogged the center of the wide lane, making it ambiguous to drivers behind me what I was going to do. No good human driver would have done that.
Overall, not a noticeable improvement over v11, and perhaps a regression. I'm looking forward to v12.4 and beyond, but at this pace I fully expect L4 city-streets FSD to be at least a decade away.