I just change the gear, and the car moves. But I don't use the throttle at all. The vehicle moves itself.

This is a phenomenon known as "idle acceleration", where the engine has enough power while idling in gear to move the car forward. This is completely normal and is actually supposed to happen, just as it does in most (automatic) real life cars.

If you still want to disable this, simply enable simpleThrottle which should automatically hold the brake pedal for you when the vehicle is at a standstill.

https://en.wikipedia.org/wiki/Idle_creep

Oh, I didn't use to know this. Now I understand. Thanks so much!
By the way, I find there's other problems in the newest version:

1.There's a white flash when I get in the car.
2.When I get off, I'm caught in the land.

Had not really noticed the first issue so good on catching that, however the second one has been ticketed with #1647
👍

This first one is normal. This happens because the camera has to init and get adjusted to the player's position. I've tried to make MC not do this, but it's something funky internal that has to do with chunk updates or something that I can't do anything to fix.

I see. But I find that these problems don't happen in 22.5.0. Is it caused by something in new versions?