Published earlier this month by Bcache developer Kent Overstreet is encryption support for the whole Bcachefs file-system. These preliminary patches were published for review and encrypt the entire file-system using ChaCha20/Poly1305. There is the support currently while creating a new Bcachefs file-system but support for an existing file-system is in the midsts of being worked on. This encryption code also doesn't support per-directory encryption.
If you are at all interested in Bcache(fs) and/or Linux file-system technologies, see this mailing list thread about the Bcachefs file-system encryption support.