You have installed Apple's new macOS Catalina on your Mac, but you may have issues with the latest version. Unfortunately, you can't just go back to Mojave. To downgrade, you'll need to erase your Mac's primary drive and reinstall macOS Mojave using an external drive. If your Mac originally came with Mojave, you can skip the instructions for the external drive.
Step 1: Back up your Mac
Most importantly, create an up-to-date Time Machine backup to store your files, or send everything to the cloud, whether it's Dropbox, OneDrive, iCloud, etc. You may already have a backup before installing Catalina. If not, create one now before moving on to the next step. As mentioned before, downgrading to Mojave requires erasing your Mac's drive.
If you need help backing up your Mac, follow these step-by-step instructions.
Step 2: enable external media booting
This step applies to MacBook Pro, MacBook Air, and Mac mini models released in 2018 or later. This also applies to the iMac Pro, which was released in 2017 and newer. These devices include Apple's T2 security chip, which offers a secure boot, encrypted storage, live commands from “Hey Siri” and more.
To check if you have this chip, follow this path: Apple button> About This Mac> System Report> Controller (or iBridge).
If your Mac doesn't have Apple's T2 security chip, there is no need to enable external media booting. Otherwise, restart your Mac and hold down the Command and R keys until the device starts in recovery mode.
With Recovery Mode open, click Utilities on the toolbar, followed by Startup Security Utility in the drop-down menu. Enter the administrator credentials when prompted and select the check box next to the "Allow booting from external media" option listed under "External startup".
Step 3: Download MacOS Mojave
You need to download MacOS Mojave from the Mac App Store. The best way to get a copy is to follow this link on a Mac, as a search on the Mac App Store itself won't show Mojave.
Clicking the link should automatically load the Mojave product page into the Mac App Store app.
Step 4: prepare your drive
You will need to format an external drive to continue. Connect an external drive and follow this path:
Finder> Applications> Utilities> Disk Utility
Select your drive listed under External and click the Erase tab. Name the drive, choose the correct format (MacOS Extended or APFS), choose GUID Partition Map if available, then click Erase. Select Done when formatting is complete.
The external drive must now be bootable. Follow this path:
Finder> Applications> Utilities> Terminal
Enter the following into the terminal. Remember to replace YourExternalDriveName with the actual name of the drive you created in the formatting step.
sudo / Applications / Install macOS Mojave.app/Contents/Resources/createinstallmedia –volume / Volumes / YourExternalDriveName
After typing the command, press Enter. You will need to enter the administrator password when prompted, followed by the Y key to confirm.
Step 6: Wipe your Mac's drive
With MacOS Mojave installed on an external drive now, you can erase your Mac's drive. Do not connect the drive yet. Instead, restart and hold the Command and R keys until the device boots into recovery mode.
Then click the Disk Utility option and click Next. In the screen below, select your Mac's primary drive and hit the "Erase" button. Follow the instructions to choose a drive name, file format, and GUID partition mapping.
Step 7: install Mojave
If your Mac came with macOS Mojave, restart and hold down the Shift, Option, Command, and R keys at the same time. This will automatically install Mojave from an image that is on a dedicated partition.
Otherwise, connect your Mac to the internet, connect the external drive and restart from the Apple icon in the top left corner. Hold down the Option key as your Mac restarts.
The following screen shows a list of the startup disk options. Select your external drive that contains the MacOS Mojave installer. Then click Continue.
Step 8: use Time Machine
Now that MacOS Mojave is up and running, you'll want to use Time Machine to restore your settings and files to what they were before Catalina.
Restart the Mac and press and hold the command and R. Keys to enter recovery mode. Press the Restore from Time Machine backup Option listed in the MacOS Utilities pop-up window. click Continue to enter this mode. Next comes another Continue Button that you use to confirm the information.
Start restoring the backup by choosing your backup source. Finally, select the latest Mojave backup to continue.
As with any other operating system, your macOS can run into a number of problems. Perhaps you don't like aspects of the Catalina update, or you run into bugs you didn't have with Mojave. Either way, our guide will get you back to base as quickly as possible, even if it's more intense than a few clicks. Fortunately, Apple makes it easy to back up your information and share things – even if you drop the latest operating system and come back to Mojave.