I have been waiting for this feature for so long...you can only encrypt bits and pieces from a note - you can't for example, encrypt the whole note, either via Cmd + A (Select all), nor through manual select...
Apparently you need to encrypt bulleted points singularly...this is plain ridiculous and it's the reason I won't be renewing my subscription.
It's a very reasonable feature that customers have been asking for years - at this point it's legitimate to believe Evernote is just not listening.