Biggest Oscar Snub
Yes, Amanda Seyfried, No Other Choice and Jesse Plemons got screwed, but to my mind the biggest Oscar snub was the brand new Achievement in Casting award not honoring Richard Linklater's Nouvelle Vague.
Not only do they nail Godard (Guillaume Marbeck), Seberg (Zoey Deutch) and Belmondo (Aubry Dullin), but found virtual doppelgangers (physically and behaviorally) for many of the supporting cast including, crucially for verisimilitude, well-known influential figures from the New Wave (Bresson, Melville, Becker, Chabrol, Rivette etc.).
Maybe this is a semantic thing, and a problem with a firm definition for the new category. Yes, Sinners has a great cast, Hamnet has a great cast, but the films are largely populated with well-known, successful actors that seem more or less born for the roles. But this is a "Best Casting" award, not "Best Cast." The art of casting is not just to match the inevitable actor with the inevitable part. It is to find that miracle fit of face and physique and talent that populates the film with texture and truthfulness. Nominees The Secret Agent and Marty Supreme actually do this very well, too. But nothing will top the achievement of Linklater's film.