That's the cool thing about BIP-38; even if someone has seen your private key (let's say, for example, someone writes it down during production), they would still need your passphrase in order to transact on the account. Ballet uses 2FKG, which means that the two critical private key components (private key and passphrase) are generated in geographically segregated locations. For more information: www.ballet.com/2FKG-graphic/

We’re talking about BIP-38, a standard to encrypt and decrypt private keys w/ a passphrase

github.com/bitcoin/bips/blob/master/bip-0038.mediawiki

Your definition of encryption, “involving taking a plaintext message and using a specific algorithm (along with a secret key) to transform it into ciphertext, which is unreadable without the corresponding decryption key”

Wouldn’t the corresponding decryption key be the passphrase, ie the BIP-38 standard?