RIP BACK TO MY MAC
FEATURE WILL NOT APPEAR IN macoS MOJAVE
Back to My Mac, the macOS feature that lets you connect to your other Macs over the internet, has been phased out in Mojave. Apple lists alternatives at bit.ly/mfmjbttm. They include using iCloud Drive for access to files, but there has been no increase on the 5GB iCloud storage space provided for free, so that may require you to pay for more.