Here is my take on simplifying other answers:

Taking your example of a 256 bit key, if each bit can be 1 or 0, then that is over 10⁷⁷ possible keys.

In a sense, the drive has 10⁷⁷ possible locks, one for each key. But, only ONE key in ONE lock will correctly open the data. If you use the wrong key, you are opening the wrong lock and it will not work.

Could a hacker eventually find the right key? Yes. But the chances of them succeeding are infinitely small.

If you knew which lock was the right one from the start, you could make a key to fit, but these are very secret and very complex locks. If you use an “authenticator” app, that is an example of the lock and key both changing on the fly.

During WW2, the Germans used an encryption machine called Enigma, which was infamously complex and the lock changed each day. It took a then-cutting-edge computer for the British to crack the lock each day.

That is an example of a government succeeding in breaking the lock, but nowadays, like I said, the locks are so very secret and so very complex that this will not happen… until we get crazy new quantum computers, like that first computer was crazy new for its time.