If parking mode comes on, you can manually shut it off by pressing and holding the power button for a few seconds.
I prefer the current implementation in that if it always comes on automatically, I shut it off manually when I don't need it by pressing and holding the power button for a few seconds rather than a manual on/off switch.
The risk with a "manual" switch is that you may forget to manually turn it on at a location where you actually need it and then something unfortunate happens to your car.
Again, for me it is always better that it comes on by default after I turn off my car, and before I get out of my car I will both hear a noise and see the screen indicating to me that parking mode being activated. If at that point (ex: personal garage to house, drive way to house, etc...), I determine that I do not actually need it then I manually shutoff the dashcam by pressing and holding the power button for a few seconds.