12 hour shifts aren’t all that terrible, as long as you actually get off on time and are paid well for working the appropriate amount of time (whether that’s 3/4/4/3 or 5/2/2/5, or 2/2/3/2/2/3, or any other schedule that gets you close to the standard hours per week). I’ve done 12s for about a decade, and haven’t had any problems with it aside from occasionally running into schedule issues because it’s hard to predict what day you’ll be working/off without calculating which week of the pay period it is.
It all returns to how much work you have to do in those 12 hours. Having even a few minutes of downtime repeatedly throughout a shift has been going the way of the dodo, and that’s going back to the original point of poor pay and fewer people to do everything needed.