Apple has very recently announced that all support for Back to My Mac will cease by 1 July 2019.

Back to My Mac was one of the existing features which was lost when upgrading to macOS Mojave, but continued to work with previous versions of macOS. Instead of making a separate announcement of this change, Apple has merely amended the original support note, which previously only referred to its loss in macOS Mojave.

Its first paragraph now opens:
“As of July 1, 2019, Back to My Mac service is not available in any other version of macOS.”
In which “any other” clearly refers to all previous versions of macOS in addition to Mojave.

The article also suggests, as it did before, the use of iCloud Drive, screen sharing, and Apple Remote Desktop as substitutes, although the latter hasn’t had any updates for a long while now despite being a paid-for Apple product.

If you’re currently relying on Back to My Mac services, you have just under a month to make alternative arrangements before losing access to it altogether. I trust that you’ll all contact Apple Support for help, so that the effect of this decision is made known to Apple loud and clear.

Back to My Mac was introduced in Mac OS X 10.5 in October 2007, and four years later was incorporated into iCloud.

(Thanks to MacRumors for drawing attention to this changed Apple support note.)