I am curious to know what kind of encryption is offered by APFS. Is hard disk encrypted by default? (If so, does it ask your password in the beginning while installing macos high sierra?) I have also heard that APFS supports single file or directory encryption. Has anyone tried it? How can we achieve it?
I don't know, sorry. There's also per-extent encryption. See https://forums.macrumors.com/posts/23019603 and other posts under Introducing Apple File System (APFS). I enabled FileVault with APFS with 17A264c. With fdesetup(8), not with System Preferences. Encryption is optional.