Yes, the nRFCrypto library does exist.
What do you mean with “PlatformIO has put a custom library.json”? The original (and included in the non-forked-by-you) Adafruit_nRFCrypto dependency does not have that. What logic you changed is a bit hard to follow since you just added the whole library instead of a change history - but I also don’t think there is much needed in terms of logic since it works in the original library with my board.
Side-note: I added lib_ldf_mode=deep in the application platform.ini [env] which seems to have fixed the crypto dependency, just now breaks a different (application, not framework-)library dependency/linking (again, it gets downloaded correctly but not found during compilation ;))