Keep in mind the gravity mechanics are different. In Mario Kart 64 you couldn’t fall straight down if you where moving.
Now another thing to factor in: That downwards drop where you where supposed to be able to hop off is now a Gravity Section. Even if the MK64 Gravity was still existent, you would be falling “Backwards” and would miss the target section.
Notice how there is a gliding section right before the finish line? If you are able to use a mushroom to maintain your momentum just as you pass the finish line, you should be able to make a sharp left in the air and glide down in the same way you would to make the shortcut back in MK64. It’s dangerous, could require more than one mushroom, and can easily be cock-blocked by the devs, but it just might work.