The "Go back" feature is the easiest way to return to your previous Windows 11 installation without losing your personal files. It is available if you upgraded within the last 10 days and the previous installation has not been removed.
Open Settings > System > Recovery, then under Recovery options, select Go back (if available) and follow the prompts. Your personal files are preserved, although apps and updates installed after joining the Insider build may be removed.
If Go back is unavailable because more than 10 days have passed or the previous installation has been deleted, there is no supported way to downgrade to Windows 11 while keeping your apps and files. Running Windows 11 Setup from an ISO does not support an in-place downgrade from a newer Insider build to an older Windows release.
In that case, you will need to back up your personal files and perform a clean installation of Windows 11. You do not need a physical installation disc. Download the Windows 11 installation media or ISO from Microsoft's official website, create a bootable USB drive (if needed) using the Media Creation Tool, boot from it, install Windows 11, and then restore your backed-up files.
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hth
Marcin