If the NSA created SHA256, can they crack it as well?

Barring some mathematical or quantum computing breakthrough the rest of the world doesn't know about: Probably not.

Cryptographic hashing algorithms rely on the property that a verifying a solution is easy but finding a solution is hard (P vs NP).

These algorithms are open. Everyone can review and test them. If SHA256 has a flaw that allows the entity that created it to crack it then it's quite likely others will find about it.

That said, it's possible but less likely that the creators of SHA256 have hidden such a flaw on purpose and that flaw as of now has remained undiscovered.