From Xojo Documentation
Encrypts the database using encryptionKey as the password. If you are already connected to an encrypted database and call Encrypt with an empty string, the database is decrypted.
AES-256 encryption is used starting with 2018r1. Before that, AES-128 encryption was used.
If you have a database that was previously encrypted as AES-128 and would like to switch to AES-256, first remove the encryption using Decrypt and then encrypt it again with Encrypt.