Help-how to revert to previous OS

Downgrading to an earlier macOS version is not a task to be taken lightly. It's easier and wiser to work through any problems you are experiencing than trying to downgrade macOS.

Before you attempt to downgrade your Mac, you must first cross your fingers, kiss the St. Christopher and hope all goes well on your journey backward.

Downgrading requires that you format the drive to erase all the data on the Mac, reinstall the older OS and finally restore your files from a backup made prior to the installation of the newer OS. Additionally, the Mac’s firmware may also have been updated when the newer OS was installed, potentially requiring you to Revive or restore your Mac in DFU mode. using a second Mac.

If all that sounds complicated and risky, you understand the reality.

1) Backup your files to an external disk with  Carbon Copy Cloner  or  SuperDuper! 

2) Download the older macOS version and create a bootable USB installer for it on a USB flash drive. This is insurance in case the Mac can’t/won’t boot in recovery mode.

3) Start up your Mac in macOS recovery mode. 

• a) Launch Disk Utility and format the internal drive. Select the GUID partition scheme, the APFS format and name the drive “Macintosh HD”.  This step will erase all of your stored data from the drive. Quit Disk Utility.
• b) Launch Reinstall macOS… and follow the prompts to select the destination drive - Macintosh HD - and begin the reinstall process. Reinstall macOS  
• c) If Reinstall macOS… doesn’t offer the OS you want, you can now use the bootable USB installer that you created.

4) Restore items backed up with Time Machine on your Mac from the backup made before your upgrade to Tahoe, or restore your files from the CCC or SuperDuper! backup you made before you started the downgrade.

Hint: It’s easier and wiser to work through any problems you are experiencing than trying to downgrade macOS.

Crabitha wrote:

Can someone tell me how to switch back to previous OS on Macbook Air M1?

Tahoe has slowed everything on my computer. Maybe my system is too old for it.

I would like to return to previous OS.

Is that possible?

It is like more likely you have some third party app or hardware driver that is causing some issue. Many apps will have code that runs in the background and sometimes an OS upgrade will make them go ballistic because they are are compatible. Sometimes the apps themselves will have issues with upgrades.

The first thing to do is to determine if all the apps you are currently using are up to date and macOS Tahoe compatible.

Check Activity Monitor for CPU and RAM load when the running slow. Also check for high disk access activity.

FWIW, I have an M1 MacBook air with only 8GB of RAM and Tahoe and it i working just as well as it did before the upgrade.

I agree with @D.I. Johnson, that is would be better to try & sort out the issues with Tahoe before trying to downgrade the OS. If you wish to troubleshoot the Tahoe system issues, then run the third party app EtreCheck and post the complete report here so we can examine it for possible clues. Also, please provide details on the issues you are having with Tahoe.

How to use the Add Text Feature When Posting an EtreCheck Report - Apple Community

Note: Step 4 of D.I. Johnson’s correct answer is crucial. If you don’t have a backup from before the OS upgrade you can wind up being worse off than before you reverted. If you don’t have a complete backup from before your OS upgrade and you insist on reverting the best option is to install all the software manually rather than use TimeMachine.