Downgrade from Safari 12 to Safari 11 [duplicate]

Solution 1:

You are on the right path and so close.

Now just tell your system NOT to Auto update.

Open Apple Store in System Preference

and disable Auto update

Alternative method:

OK, lets use "sneaky" method,

Disconnect from Network, WIFI, (cut the cable ... just kidding :) so it can not update.

That should give you time to change the auto update settings.

Solution 2:

Go to Mac App Store page for macOS High Sierra and download the installer.

Create a bootable installer for macOS High Sierra by following the instructions in the support document, How to create a bootable installer for macOS:

Use a USB flash drive with at-leat 12 GB of free storage space and run the following command:

sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ High\ Sierra.app

Once you have the installer ready, use it to install a fresh copy of macOS High Sierra. Once installed restore your data from Time Machine backup.

Now turn-off automatic updates in System Preferences and manually check for updates. Under Updates in Mac App Store do not choose to update Safari.