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How to downgrade from MacOS Big Sur to Catalina

The MacOS Big Sur update, while filled with improvements, is not without its difficulties: Users have come across a variety of bugs, including problems that temporarily bricked their Macs, video porting issues, sudden slowdowns, and more. Some users have preferred to return to MacOS Catalina entirely, and wait until all the major bugs with Big Sur have been dealt with.

If that describes you, there is a way to roll back Big Sur and return to the more pleasant Catalina OS, although it does take the right procedure. Here’s what you need to do.

Step 1: Back up your data

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If you haven’t already done so, now is the time to back up your data. You can always use Time Machine to back up data on a Mac, but buggy operating systems can make Time Machine difficult to use, so it’s smart to find a backup method that doesn’t rely on MacOS.

An external hard drive comes in very useful here. If you have lots of iCloud space, you can also store all important files in iCloud for easy retrieval if necessary. Oh, and if you’re on a MacBook, this is also a good time to plug your Mac into a power source and set up where you can stay for a while.

Step 2: Shut down and enter Recovery mode

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Close all your apps, and complete a full shutdown for your Mac. You can either press the physical power button or select the upper-left Apple icon and choose Shut Down to begin. Your Mac may take a while to fully shut off. If a bug pops up and freezes your Mac during this process, hold down the power button for several seconds to force a shutdown.

When your Mac is off, disconnect any accessories except for your mouse and keyboard. Then press the power button to turn it back on. When your Mac is powering up, immediately press and hold the Command and R keys, until you see the Apple logo appear. Now release those keys, and your Mac should enter Recovery mode. You will know this worked if you see the window called MacOS Utilities appear.

Note: If you have a Mac with an Apple silicon chip, pressing and holding the power button should take you to a startup menu, where you should choose Options instead.

Step 3: Look for a Time Machine backup

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Examine MacOS Utilities. The first option should be to Restore from Time Machine Backup. Start by selecting this option, then choosing Continue, and your Mac will search for any Time Machine copies of your OS.

Here’s where things get a little tricky: If you know you have a Time Machine copy and it is stored on an external hard drive, you need to plug in that external drive before choosing this option. If you aren’t sure if you set Time Machine to make regular copies, let your Mac search and see what it finds.

If your Mac does return a Time Machine backup, take a look at what operating system it is and the date of its creation. You will want a Time Machine backup from just before you installed Big Sur. If a copy looks like what you need, select it, and select a destination disk where the backup will be stored. Then select Restore, and choose Continue when prompted. You may be asked to choose categories of information to restore — if so, simply choose all of them.

Step 4: Use the Reinstall MacOS option as an alternative

MacOS Utilities
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If you haven’t been using Time Machine and don’t have any backups, there’s still another option you can try. Back out to MacOS Utilities, and this time choose the Reinstall MacOS option. Select Continue, and enter your Apple ID. Your Mac will then search for an internet connection, which is required for the reinstall process. If your Mac is having trouble connecting to Wi-Fi, you may need to run an Ethernet cable from your router to your Mac for a wired connection.

Important note: This process is effective if Big Sur is having trouble booting up after a buggy installation. If Big Sur is already installed and you’ve been using it, it may just get reinstalled again — which isn’t what we want. There are ways around this!

  • First, try starting up in Recovery mode again, this time using the Alt + Command + R keys. This should make sure the Reinstall option is set to the version of MacOS that your Mac came with. If you have a Mac that is only a year old or so, this should be MacOS Catalina, which fixes your problem.
  • If your only option is to reinstall Big Sur, you will need to create a bootable installer with MacOS Catalina instead, and use it as a startup disk. Apple has specific instructions for this process, which is not complicated but will require a 12GB flash drive to work.

When your Mac starts reinstalling MacOS Catalina, it’s going to take an hour or two to finish, so stay patient. The good news is that your files and apps — unless corrupted — should be saved and ready after your Mac is done.

Step 5: Erase your Startup Disk if necessary

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If you’ve tried everything but your Mac is still experiencing serious malfunctions that make it unusable, you should try erasing the startup disk entirely. Choose Disk Utility at the MacOS Utilities menu, select Continue, and then choose your Startup Disk from the menu options. Not sure which disk it is? If your Mac is still operational, you can go to System Preference and select Startup Disk to take a look.

Now select Erase. Your Mac will let you choose which format you want to use — choose APFS. If asked about partitioning, choose GUID Partition Map. Confirm the process, and the startup drive will be erased, allowing for a cleaner MacOS Catalina install. Since many Mac setups use an additional disk for storing personal files, these may largely remain intact.

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Tyler Lacoma
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