TNG’s post-nuclear hellhole visit was to the 2070s; which does seem to contradict the later TNG narrative that First Contact was in the 2060s, but, then, it’s easy to imagine that meeting the Vulcans and inventing the Warp Drive did not immediately make the entire planet a paradise.
VOY’s seeming contradiction in its time travel adventure was with TOS’ assertion that a large-scale war across significant parts of Eurasia with genetically modified supermen took place in the 1990s and there seemed to be no sign of it in 1990s L.A., which, one, VOY’s time travel was after a change in their timeline had already happened in the 1960s that they were going to try to figure out and repair it, and, two, even if that shouldn’t have averted the Eugenics Wars, it is also entirely believable for there to have been a large-scale war across significant parts of Eurasia with genetically modified supermen in the 1990s and for Los Angeles to appear completely unaffected.
EDIT: Time travel‘s still pretty dangerous though for a storyteller in this sense, because even when you don’t contradict yourself you might seem to and that might turn some people off. Though, like you, a lot of people also won’t mind. Even though in practice Star Trek does self-contradict in a number of ways, in the vast majority of cases nobody minds — no one who isn’t a raving misogynist is really defending TOS proclaiming that women can’t serve as starship captains and so thus denouncing that ENT and DSC have female starship captains chronologically earlier.