I have a question to add. If say I have a bitcoin wallet that is unencrypted, I make a backup of it and then encrypt the wallet. Years later, I dig up the backup and import it, will the backed up wallet get encrypted aswell or will it be usable and unencrypted?
You can only use a fully decrypted private key. If you are able to import an encrypted wallet it's because the wallet software likely can detect what kind of encryption and then proceed to ask you for the passphrase to decrypt it (e.g. a BIP38 encrypted private key).
Honestly, your backup should be the encrypted version of it unless you seriously have troubles remembering your passphrase. If you're using some ridiculous 12 word passphrase, then write it down, but keep it separate. Otherwise, you're better off with a plaintext private key that you keep safe.