if possible can someone share the steps to reinstall the wonderful Sequoia and what’s necessary after the install is complete?
If you don't have a backup made prior to installing Tahoe, it is much more difficult. You will need to manually copy all of your data to an external drive and then manually copy it back into reinstalled Mac. If you have stuff in iCloud Drive, you would not need to back that up, just sign back into your Apple Account. Same for any services you have linked to iCloud like iCloud Photos, Music, Contacts, Mail, etc. If you have any of that type of content not synchronized with iCloud, you must export it out of the host application and then import it back into those programs. For Photos, Music, and anything else that stores additional metadata, you will lose all of the metadata you entered (like keywords, location info, faces, song/album info, etc).
Most macOS these days updates the firmware on the Mac for the new OS. I don't think reinstalling an old OS will revert the firmware, so this all may not work. I just don't know how that is handled.
- Download Sequoia and create a Bootable USB Installer from that download. There are instructions on how to get an older macOS version in that linked article. When you format your USB stick for the installer, just name the volume, "My Volume." That way, there is no need to alter the command, you can just copy and paste the command from that article.
- Start up from the Bootable USB Installer. There are instruction in the above linked article on how to do that.
- Once booted into the USB Installer, open Disk Utility. Erase your startup drive. When booted into the USB Installer, you are in Recovery—do not restart into Recovery on your Mac or into Internet Recovery. You can name the new volume anything you want. "Macintosh HD" is the factory default name.
- Once erased, quit Disk Utility and choose Install macOS. Follow the instructions and install on the volume you created when you erased the drive.
- When your Mac restarts into macOS Sequoia Setup Assistant, choose to Migrate from a Time Machine backup. If you had inherited your backup into Tahoe, when you select the backup you will need to expand the list of backup sets and choose the date/time you last backed up Sequoia. If you select a backup that was made with Tahoe, it will tell you that you must reinstall macOS to Tahoe. Back up and choose an earlier backup set.
If you have a non-Time Machine backup, you may still be able to Migrate from that backup, but I don't know how to do that. Contact your Backup provider for instructions.
