What john format should be specified to crack an 18 character Windows password?

LANMAN hashes split the password into two 7-character halves before hashing, making it impossible to represent any password longer than 14 characters.

SHA256 is a general-purpose cryptographic hash and is not a Windows password storage format recognized by John the Ripper for SAM/NTLM hashes.

The NT hash format in John the Ripper uses MD4 applied to the full Unicode representation of the password, supporting Windows passwords of any length including 18 characters. LAN Manager hashes split input into two 7-character chunks and therefore cannot store passwords longer than 14 characters. NT is the correct format for cracking NTLM password hashes stored in the Windows SAM database or extracted from memory.

MS-CACHE (Domain Cached Credentials) is a separate hash type used to store cached domain logon credentials locally and is distinct from local account NT hashes.