Boot to Internet Recovery (Option-Command-R or Option-Shift-Command-R) to prepare to downgrade to the version of macOS that came with your Mac or the closest version that’s still available.
Erase volume group
Open Disk Utility and select “Macintosh HD”. Select the “Erase Volume Group” (not just the volume “Macintosh HD”). You may have unexpected results if you do not select ”Erase Volume Group”. When complete, quit Disk Utility.
Reinstall macOS in Internet Recovery
Click on Reinstall macOS and follow the onscreen instructions. If Find My was enabled on the Mac running macOS Monterey Beta, you will need to activate the Mac when the reinstall process completes. At the end of the activation process, you will be prompted to restart the Mac. More details about reinstalling macOS are available here.
Follow the macOS Setup Assistant
At the appropriate time, select the option to restore data from a Time Machine backup. Select the backup that was completed at the start of this process to restore the Mac’s data.