Can you crack SHA-256?
There is a large difference between being able to produce the preimage for a single SHA256 hash for which you may know certain factors like length, character set, etc., and being able to break SHA256 as a whole.

Short inputs are naturally more vulnerable to brute forcing, which is why SHA256 is not a recommended hash for password storage - instead, hash functions that are deliberately designed to be slow and adjustable, such as bcrypt, are used where the input size may be small enough for practical brute forcing of hashes like SHA256.

In all applications of SHA256 in the Bitcoin Protocol, all the inputs are large enough to make a brute force attack impractical.