Oh, that's a fascinating topic! False protagonists really mess with your head in the best way. I was utterly duped by Ned Stark in 'A Song of Ice and Fire'. You spend that whole first book seeing the political mess through his honorable, dutiful eyes, believing he's our guide. His execution isn't just a plot twist; it fundamentally rewires the story's entire moral compass and shifts the protagonist mantle onto a bunch of fractured, younger characters. It tells you right away this isn't a story about a noble hero fixing things.
Another classic that comes to mind is Marion in 'Psycho'. The film's based on the novel, but the principle is the same. You follow her anxiety, her theft, her flight to the motel, believing her fate is the central mystery. When she's killed off so abruptly, it's a brutal transfer of narrative focus to Norman Bates, forcing you to re-evaluate everything you thought the story was about. It's a masterful bait-and-switch that redefined suspense.
A more recent, and brilliantly meta, example is in 'If We Were Villains' by M.L. Rio. The opening frame has Oliver getting out of prison, suggesting his story is the core. But as the flashback unfolds, the narrative subtly but irrevocably pivots to focus on the tragic, performative downfall of his friend James, making you realize you've been watching the wrong character's tragedy all along. Oliver was just the narrator, not the true tragic hero.