The Whale is shot in a 4:3 aspect ratio, which makes the dimly apartment Charlie is confined to feel claustrophobic, but I also get a sense of it feeling more personal with the nearly square image making us focus more on each character and less on what surrounds them. It brings them closer to us.
Once Upon a Time in Hollywood is shot in a 2.39:1 aspect ratio. Huge, cinematic images of 1960's Hollywood and the expanse and ambition of the sets, storyline, and characters.
This technical choice really affects the feel of the story. The Whale is not cinematic, it's personal. And it needs to feel personal to get the full effect. Placing Tarantino's work into a small box would detract from the scope and magnitude of the universe it which exists.