For Windows 10/11:
- Press Windows+I to open Settings.
- Click Update & security.
- Click Recovery on the left-hand side.
- Under Go back to the previous version of Windows, click Get started.
You only get a certain amount of time to roll back after upgrading, I believe after 10 days Windows will clear away the backup. The backup can also be deleted when running Disk Cleanup with the Previous Windows installation(s) option selected.
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