Apple should bring APFS to Time Machine and disclose full APFS specifications for developers like Alsoft to make DiskWarrior for APFS. Stuck on macOS 10.12 Sierra until then!
You are not really "stuck" on Sierra.
You can install High Sierra without switching to APFS.
Make sure the installer file is in the /Applications folder, run the command below from the terminal. (These instructions were found in this forum, sorry I cannot give credit where it is due)
/Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall --applicationpath /Applications/Install\ macOS\ High\ Sierra.app --agreetolicense --converttoapfs NO --nointeraction
To specify what drive to install macOS High Sierra on, other than the startup drive, you need to add the following to either of the Terminal command lines listed above:
— volume /path to the volume you wish to use
An example for installing macOS High Sierra on a drive named HighSierra without converting the target volume to APFS would be:
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall –applicationpath /Applications/Install\ macOS\ High\ Sierra.app –converttoapfs NO –volume /Volumes/HighSierra
This would force the installation to occur on a volume named HighSierra. An easy way to enter the actual pathname to the drive you wish to use is to enter the command in Terminal without the actual pathname, so the command would end after — volume (make sure there’s a space after the word volume). Now drag the drive from the Finder and drop it on the Terminal window. Terminal will add the actual pathname to the drive for you. All that’s left to do is press enter or return.
The — volume switch will also work when you wish to force a conversion to APFS, as shown in this example, which will convert the drive named HighSierra to APFS and install the new version of macOS:
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall –applicationpath /Applications/Install\ macOS\ High\ Sierra.app –converttoapfs YES –volume /Volumes/HighSierra
By using the startosinstall command from within Terminal, the choice to convert to APFS or leave the target drive’s format unchanged is entirely up to you.