Back to My Mac will not be available on macOS Mojave. You can get ready now by learning about alternatives for file access, screen sharing, and remote desktop access.
An alert popped up on my Mac this morning warning that the Back to My Mac service was ending soon and linked to a support article on Apple’s Web site. It’s too bad, I really enjoyed the service, but it’s not like you don’t have options—Apple details everything in the support document.