I could find this Microsoft Answers post where someone suggests doing a custom install (which would then move/retain your old files to another folder):
Keeping old data when installing Windows 11 from a USB
But not sure if that is what you would want to do though. I am still holding off accepting the Win11 upgrade prompt and still running Win10 for now.
Also found this page which might help and seems to list the options:
Learn about the recovery options in Windows. Find out how to reset your PC, go back to a previous version of Windows, or use media to reinstall Windows.
support.microsoft.com
Either way, I would recommend creating a backup / image or copy any files you can't lose before starting anything.