Removing Monterey and reload an older version of the system software from Time Machine

Follow the advise from previous posting above >> First.

As a Last Resort and mean Last Resort.

" Scorched Earth Method  "

This method will WIPE ALL Data and there is No Recovery - Period.

>> Only works on Intel Based Apple Computer <<

To perform this action will require booting from a Bootable Installer. 

The Bootable Installer can Only be performed on an Apple Computer 

This will have to be performed from a Qualifying Computer to run the version of macOS to be made on the Bootable Installer. Example : Bootable Installer of Big Sur would have to be done on a computer that Qualifies to run Big Sur.

Notation: If the computer being used to perform this action is Too New or Too Old to qualify to run the version of macOS - this computer can not be used.

Alternative is, to gain access to a Qualifying Apple Computer from a family member, friend or associate.

1 - Shutdown computer and disconnect all external drive Except the newly created Bootable Installer.

2- Restart and immediately hold the OPTION key until the Startup Manager appears and choose the USB Drive. 

3 - It will present options >> Disk Utilities >> View >> View ALL attached Drives. 

4 - Choose the Upper Most Drive ( not the volumes indented and list below ).

5 - The drive normally is called Apple Media or Apple SSD - that is the drive to Erase and format as APFS with the GUID Partition Map. This applies to macOS 10.14 Mojave and above. 

5A - Formatting for macOS 10.13 High Sierra and below requires HFS Journaled with the GUID Partition Map

6 - Once that is done >> backup out of Disk Utilities and choose install macOS. 

7 - Follow the prompts and it may automatically reboot several time. 

8 - Upon a final reboot - Setup Assist will present with the newer version of macOS.

Humbugaway wrote:

Hello,

I want to downgrade my OS from Monterey as I can't use any of my software apps since it was loaded on and it is causing many issues with speed and so on. I tried to go backwards by using my Time Machine back-up but the external drive with TM on is partitioned and the restore button in Time Machine was greyed out so wouldn't allow me to click it.

I don't know what to do next because my Mac is basically useless to me except for the internet and mail and I can't do any work on the software programmes I have because of incompatibility with Monterey.

I know, I know, maybe I should have thoroughly checked all that before upgrading but I was on a chat with an Apple agent who walked me through it and never mentioned that nothing would be incompatible. Now I am in a mess.

My question is... am I able to downgrade to an older OS if I have a partitioned external drive (half storage, half back-up). If yes, then how do I do it please?

Screen grab below of my Mac details. Thank you in advance.

https://discussions.apple.com/content/attachment/c8e6a8fd-7030-4356-8b2f-b893f02505f3

It can be done. One can only Roll Back as far as the version of macOS that came installed on this computer when it was New.

This method will WIPE ALL Data and there is No Recovery - Period.

>> Only works on Intel Based Apple Computer <<

To perform this action will require booting from a Bootable Installer. 

The Bootable Installer can Only be performed on an Apple Computer 

This will have to be performed from a Qualifying Computer to run the version of macOS to be made on the Bootable Installer. Example : Bootable Installer of Big Sur would have to be done on a computer that Qualifies to run Big Sur.

Notation: If the computer being used to perform this action is Too New or Too Old to qualify to run the version of macOS - this computer can not be used.

Alternative is, to gain access to a Qualifying Apple Computer from a family member, friend or associate.

1 - Shutdown computer and disconnect all external drive Except the newly created Bootable Installer.

2- Restart and immediately hold the OPTION key until the Startup Manager appears and choose the USB Drive. 

3 - It will present options >> Disk Utilities >> View >> View ALL attached Drives. 

4 - Choose the Upper Most Drive ( not the volumes indented and list below ).

5 - The drive normally is called Apple Media or Apple SSD - that is the drive to Erase and format as APFS with the GUID Partition Map. This applies to macOS 10.14 Mojave and above. 

5A - Formatting for macOS 10.13 High Sierra and below requires HFS Journaled with the GUID Partition Map

6 - Once that is done >> backup out of Disk Utilities and choose install macOS. 

7 - Follow the prompts and it may automatically reboot several time. 

8 - Upon a final reboot - Setup Assist will present with the newer version of macOS.

9 - Then, you can use your Time Machine Backup Drive & use Setup Assist on the First Boot-up.

To restore an entire system, you have to boot into Recovery and Restore.

Revert your Mac to a previous macOS version - Apple Support

I probably misunderstood your initial question, but the way it read to me, was you used Enter Time Machine and on the time machine interface, you tried to click restore, which was disabled.