Good analogy. Would you run your car over a cliff or would you know about an invisible something if you were told that?
You took the analogy out of context. The comparison was focused on the meaning of
"fastest means possible" and whether there is a direction component to it. It was not focused on the rest of the spell and driving a car is not the same as movement in 5E. That said to answer your question:
To start with we need to discuss the ramifications of driving off a cliff. In D&D, jumping off of Mount Everest and falling 33000 feet will not kill most enemies PCs will face at level 2 and above. So if I could drive my car off a cliff and survive 90% of the time there is not an imperative not to drive off the cliff, especially if I am fleeing from what I perceive as likely death.
That said, assuming that we are in the real world and it actually would likely might kill me - If I did not drive off the cliff I would not be following the literal directions, and if I had agency to control what I did might stop and I might say
"I didn't follow your directions, I stopped so I did not go off the cliff" Heck I might even say
"I don't want to drive at all, I will just go make a gin and tonic and hope for the best". If I am being magically compelled though, as in the spell I don't have those options and off the cliff I go!
There are not "invisible walls" IRL, so it is a bit difficult to answer, but if there were and there was magic causing me to get as far away as possible, then yes the car would go around the invisible wall. Think of it like you are in a Tesla and it has the maps with all the walls and all the cliffs and the corrupted softwar must just move you as far away as possible, period, whether you know the best way or not.
Let's reword that anaolgy to better fit:
"If you fail the save you drive away from NYC by the fastest available means." and this MUST happen - off the cliff or around the wall I go.
Also just an interpretation. Wouldn't you open your garage to get the car out?
Not if all I could do is drive and I was not able to do other things like get out and open the garage (i.e. utilize) or fill up the car with gas, or change a flat tire.
Oh. I would actually not allow that, as those actions don't help you get away.
Doesn't matter. Nothing in the spell says you need to "get away" or that you can't do things that don't help you get away. You have to
move, those are done as part of moving according to the rules.
Further this interpretation puts in a logical inconsistency in your argument - you claim the target has the option to stop moving or not move as far as possible (i.e. off a cliff). So you have some level of agency to limit compliance with the thing the spell requires you to do; yet you don't have the agency to do other things that are RAW part of your move even when they don't limit compliance with what the spell requires.
Why is it I can stop at the cliff edge and not jump off, but at the same time I am not permitted to tell Clyde the Cleric to come heal me when both are part of my movement but only the first goes against what the spell compels?
Neither would I allow that.
Ok you wouldn't at your table. RAW you can. You do it as part of your movement.
Note you can not do these things with some of the other commands, but you can with "Flee" RAW.