Student or Learner
I understand that before and until are not always interchangeable.
e.g. Brush your teeth [before / until] you go to bed.
In this case, until is wrong because it sounds like you have to keep on brushing your teeth until you go to bed.
However, it seems to me they are sometimes interchangeable.
e.g. Donít get off the bus [before / until] it reaches its destination.
In the case above, are both until and before really fine?
"Get off the bus [before / until] it reaches its destination." Only 'before' works. Your own examples demonstrate that "Doing something until X" and "Not doing something until X" are not exactly the opposite of each other because 'until' doesn't work like that.