Apple has announced that its Back to My Mac feature will not be supported in macOS 10.14 Mojave, when it is released shortly.
In that announcement, it provides links to articles detailing the services which it recommends users change to instead. These are iCloud Drive for file sharing, accessing another Mac using built-in screen sharing, and managing your Mac remotely using Apple Remote Desktop (which costs £74.99 from the App Store, and hasn’t been updated since February 2017).
Rumours suggest that Mojave may now be less than a month away. If you are using Back to My Mac and intend upgrading to Mojave, you might like to start switching to those other services now.
Back to My Mac was introduced in Mac OS X Leopard, in 2007, and since 2011 has been included in iCloud services.
(Thanks to Sqwarq for drawing attention to this, because I don’t recall Apple announcing it clearly.)