In aircraft, legal liability is unaffected by whether the autopilot is on; the pilot in command is responsible no matter what. I see no reason for cars to be any different.

What happens when one of the tools is malfunctioning? Say autopilot doesn’t turn off? Is it still blamed on captain?

Yes, because there are usually no less then 4 separate ways to turn it off (AP disconnect, trim switch, circuit breaker(s), servo override) and this includes small GA airplanes. The autopilot does not fly the airplane on intuition. It flies based on the way the pilot programmed it, malfunctions are expected and trained for and memory items are required for quick disabling of malfunctioning systems.

I’m a pilot and airplane owner.

Autopilot not turning off is not a realistic scenario. There are multiple ways to turn them off, including cutting power entirely by pulling a circuit breaker. You'll often see a colored plastic ring attached to the AP breaker for this exact reason.