Amateur Titanic historian here. While it’s not the most accurate depiction of the sinking (that’d be A Night To Remember, which, while really good, I don’t like nearly as much as Titanic), Titanic is more-or-less pretty accurate. Something that I don’t think gets enough credit is that the movie, because of better CGI VFX/bigger budget, gets into the mechanics and physics of how the ship actually sank. It was the first depiction to show characters going into the flooded decks. It was also, to my recollection, the first depiction to show the ship splitting in half after Robert Ballard discovered the wreck. Subsequent research has shown that maybe the ship didn’t split EXACTLY the way it was shown in the movie, but the fact it was included was in itself kinda revolutionary.

Another thing I’ll say is that, perhaps because of maturing sensibilities, Titanic doesn’t shy away from uncomfortable truths about the sinking the way ANtR and other movies did. The shot of Isador and Ida Strauss cuddling in bed together as the water rises is heartbreaking (and accurate!), and it shows just how different this film is than previous depictions. Same goes for the guy hitting the propeller, or Frabrizio being crushed by a funnel. (Despite Frabrizio being fictional, that really did happen to some people. Fun fact: no one knows exactly what happened to Titanic's funnels? The best guess we have is that they were eaten by bacteria because they were made of a lighter steel than the rest of the structure of the ship.) Hell, the movie even depicts the chef who famously drank so much he survived the freezing water. Thomas Byles, the priest who stayed on the ship til the end, also gets more of a focus than he had in other versions.

The biggest omission, in my mind, is one that is at the heart of A Night to Remember but not even touched upon in Titanic: that’d be the SS Californian. The SS Californian was a nearby ship that, had they taken the signals seriously, might (key word here) have been in a position to rescue. But instead, the Californian dismissed the RMS Titanic’s emergency flare rockets for reasons that aren’t clear. (Urban legend says the SS Californian’s captain believed the rockets were fireworks for a party, but I double checked and he in fact testified that it never occurred to him that the rockets were a distress signal.) They also tried to communicate with the RMS Titanic via morse lamp, and NOT by telegraph, the preferred method at the time. (RMS Titanic’s telegraph operators Jack Phillips, who died, and Harold Bride, who didn’t, are two of the heroes of the disaster, they kept telegraphing that the ship was sinking until the last minute.) I understand why Cameron omitted it, as it takes focus off the Jack/Rose romance that’s the crux of the particular story he’s trying to tell, but that doesn’t necessarily forgive its omission.

A lot of the choices, if they’re inaccurate, seem to be for the sake of storytelling. Like, Ismay and Captain Smith probably didn't have that talk about what Ismay's expectations were in real life, it was more sort of implied. (Just having Ismay, essentially the owner of the ship, on the maiden voyage had the crew anxious to impress him.) But having a scene where they talk about RMS Titanic's speed clues the audience in about what exactly those implications are, and how they would play out in what ultimately happened. (And so Smith can have that line "I think you'll get your headlines, Mr. Ismay," which, all my fellow 90s kids know is when tape 1 ended on Titanic's VHS.) As with many historical films, they take what was probably more subtle and nuanced in real life and are explicit about it in order to clue the audience in.

Hope that was helpful! If you’re interested in a more accurate depiction, A Night to Remember is definitely worth watching, even if Titanic is ultimately more entertaining.

EDIT 1 after double-checking sources re: Californian.

EDIT 2 formatting, referring to the actual ship as RMS Titanic in order to differentiate it from the movie

EDIT 3: IMDb tells me that Cameron wrote and filmed a scene involving the Californian, but cut it for pacing issues. He said in an interview: "The story of the Californian was in there; we even shot a scene of them switching off their Marconi radio set. But I took it out. It was a clean cut, because it focuses you back onto that world. If Titanic is powerful as a metaphor, as a microcosm, for the end of the world in a sense, then that world must be self-contained."