Is a movie prop the ultimate laptop bag?

> For me, the ultimate laptop bag is one that looks nothing like a laptop bag; it should look like nothing special at all.

That sounds like almost any regular backpack then. They can also be pretty weather proof, don't need to be carried in one hand, aren't open topped showing what's inside easily, and padded. Any simple and cheap backpack would solve this exact problem but better surely, unless your desire is to be different rather than just to move your laptop from one place to another with little ceremony.

When I lived in San Francisco, backpacks were marginalized as being associated with being too poor to own a car. High-school students might carry a backpack, college students might carry a backpack, people on the bus might carry a backpack, but mostly not professionals who drove to work.

Maybe that's changed, though. https://www.youtube.com/watch?v=4zwWpqsI_3s purports to be from 02022, and in its first minute, I count 17 pedestrians of whom 4 are wearing backpacks. So maybe backpacks are mainstream in SF now.

Isn’t looking poor a good strategy for being an unattractive target for theft?

No, police punish theft from rich people, not theft from poor people.