There is a default 10 day go back option after upgrading from Windows 10 to Windows 11.
This go back option default can be modified during the 10 day period to go back 60 days.
It can be modified again up to 60 days.
If the default 10 day option passes so options to return to Windows 10 are:
1) Perform a modified custom install using a Windows 10 iso
A typical custom install is Windows 11 to Windows 11 or Windows 10 to Windows 10 after creating a Windows.old.
After the new Windows installation important files are restored from Windows.old.
In the modified custom install the Windows.old is created from Windows 11 to be able to restore files to the new Windows 10 installation.
2) Backup important files to another disk drive or the cloud followed by a clean install Windows 10
These are some links:
https://www.tenforums.com/tutorials/120352-custom-install-windows-10-a.html
https://www.tenforums.com/tutorials/148005-how-restore-files-windows-old-folder-windows-10-a.html
https://www.tenforums.com/tutorials/1950-clean-install-windows-10-a.html
https://www.tenforums.com/tutorials/2376-create-bootable-usb-flash-drive-install-windows-10-a.html
https://www.tenforums.com/tutorials/9230-download-windows-10-iso-file.html
https://www.microsoft.com/en-us/software-download/windows10
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