I've got one that's a gem and hasn't been mentioned yet, for once!
Upgrade (2018)
A guy and his wife are attacked, his wife is murdered and he just barely survives. With the help of a super-chip implanted into his body by a billionaire, he sets out to get revenge. But at what cost?
A stylish, savage techno-action film, basically John Wick but with AI chip. The ending is rightly haunting. Well worth watching!
Without spoiling too much, the ending is not entirely traumatising in my view, but it personally left me rather depressed, with an acute feeling of loss and hopelessness. Though wouldn't say that any standard trigger/content warnings apply to the ending (the rest of the movie does get rather bloody though)
Hope you enjoy it! Here's one of the spoiler-free content guides I found for it just to give an idea. Violence, blood and gore are at the top of the list, as expected ;)