How to restore MacOS from Time Machine?

MacOS will NOT restore Older macOS over a Newer MacOS unless you deliberately use Disk Utility to completely ERASE the drive.

What is being suggested is that you leave your macOS alone (or install/re-install it from fundamental sources rather than use your MacOS on the backup drive) and use Setup Assistant at first run or Migration Assistant later to get your files back.

It can restore YOUR FILEs from any backup you choose.

It can do a complete restore including MacOS if you completely ERASE your drive, but not otherwise.

LCMan wrote:

I keep getting this popup when trying to restore MacOS to a later date from my external hard drive.

https://discussions.apple.com/content/attachment/485dbe5a-7e09-4b72-ae5b-3cd6a82ba5eb

How to reinstall macOS

Recovery (both M1 and Intel) — How to reinstall macOS - Apple Support