How to revert from monterey to High Sierra on my Macbook

Do you have a Time Machine backup to Restore to/from?

https://eshop.macsales.com/blog/32972-time-machine-what-it-is-how-it-works-and-how-to-use-it-with-your-mac/

https://support.apple.com/guide/mac-help/revert-to-a-previous-macos-version-mh15216/10.14/mac/10.14

If not…

https://www.imore.com/how-downgrade-macos

This Method will Wipe ALL DATA and there is No Recovery - Period

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

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 High Sierra would have to be done on a computer that Qualifies to run High Sierra .

This means - if the computer being used has never run High Sierra or is TOO New to running High Sierra - that computer can not be used for this operation

Once that is done read on for preparing the Destination computer 

>> Only works on Intel Based Apple Computers.

Extra Special Notation regarding the Touch ID equipped Apple Computer.

About Startup Security Utility and Must Enable from Recovery Mode the ability to boot from External Drive Before Attempting 

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.

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.