Downgrade from Monterey to Big Sur

bkeltie wrote:

I have updated to Monterey but need to return to Big Sur (or earlier OS) for MBP 15" 2019 2.4GHz 8-Core Intel i9. Can anyone provide an easy step by step guide ('cause I'm simple) about how to do this? I think I need to create a bootable drive but can not find where to download the earlier versions of Mac OS. Thanks in advance

From a backup—

same as here:

Revert your Mac to a previous macOS version
https://support.apple.com/en-lamr/guide/mac-help/mh15216/10.15/mac/10.15

How to reinstall macOS

Recovery (both M1 and Intel) — https://support.apple.com/en-us/HT204904

Restore items backed up with Time Machine on Mac

https://support.apple.com/guide/mac-help/restore-files-mh11422/mac

<< need to return to Big Sur (or earlier OS) >>

Why?

Downgrading is not possible in an 'ordinary' way.

The way to do it is to have on hand at least one and preferably TWO Trusted Backup copies of all your files. ERASE your drive [this removes all your files permanently] then re-install the required version of macOS. Use setup assistant to import all your files and settings again.

This process is complex. Unless you REALLY have no other way around it, I would not recommend it.

How to create a bootable installer for macOS - Apple Support

Download links are on the support page.