You will lose files you’ve created since the upgrade if you restore an old Time Machine backup.
Connect your backup hard drive to your Mac.
Restart (or start up) your Mac while holdingCommand+R.
you could release the keys when the Apple logo appears.
The macOS Utilities window will open.
SelectRestore from Time Machine Backupand clickContinue.
When theSelect Restore Sourcewindow appears, highlight your backup drive and clickContinue.
input your user password to access your disk (if it’s encrypted).
On the next screen, snag the backup you want to use.
Look for one that has10.14in themacOS Versioncolumn.
That’s the release number of Mojave.
On the next screen, grab the destination (typically your Mac’s built-in hard drive) and clickRestore.
Your Mac will restore that backup and then restart with macOS Mojave installed.
This process will completely erase your hard drive.
Back up your gear.
SelectAbout this Macunder theApple Menu.
If theModel Namefield saysApple T2 Security Chip, you’ll have a few more steps to follow.
If not, go to Step 11. kickstart your Mac and holdCommand+Runtil you see the Apple logo.
When the macOS Utilities window appears, selectStartup Security Utilityunder theUtilitiesmenu in the toolbar.
type your administrator password if you receive a prompt.
see to it that the box next toAllow booting from external mediahas a check in it.
reset your gear again to return to normal mode.
Download macOS Mojave from the Mac App Store by going the Mac App Store and clickGet.
Connect the drive you want to create your installer on to your Mac.
You need at least 16GB on the drive to create the installer.
you’re able to alsopartition an external hard drive.
pick the drive you want to create the installer on.
SelectEraseif you’re using a new drive, orPartitionif you’re using part of an existing one.
Skip to Step 20.
Alternatively, you’ve got the option to format the drive asAPFS.
If you chose toPartition, click theplus signon the screen that opens.
ClickApplyto create the partition.
drop your administrator password and pressReturn.
PressYto erase your drive (again) and create the installer.
Disconnect your drive and reboot your setup while holdingCommand+Runtil you see the Apple logo.
When the macOS Utilities window appears, selectDisk Utilityand clickContinue.
Select your hard drive underInternaland clickErase.
Once your hard drive is empty, reconnect the drive with the Mojave installer and restart again while holdingOption.
pick the drive containing Mojave and clickContinue.
Your Mac will install Mojave and start up.
To restore your files, openMigration AssistantunderUtilitiesin yourApplicationsfolder.
Migration Assistant will close all other programs while it’s running.
SelectFrom a Mac, Time Machine backup, or startup diskand then clickContinue.
pick the drive you use for Time Machine and clickContinue.
grab the particular backup you want to restore and clickContinue.
snag the information you want to transfer, and then clickContinueto finish the process.
You’ll probably want to transfer all of the available information.
Here’s how to downgrade from Catalina to Mojave by restoring your system.
Back up your setup using Time Machine.
reset your gear while holdingCommand+Rto enter Recovery Mode.
Select your internal hard drive and clickErase.
When your hard drive is empty, restart again while holdingShift+Option+Command+R.
Your Mac will start up and implement the version of macOS that came with your box.
Restore your files using Migration Assistant, following Steps 31-36 above.
