I'm not sure why it's not offering to keep your files unless the account is corrupted. Are you using the very latest media from the media creation Tool? Try downloading the ISO, double click it to mount it as a virtual driver, right click Setup to Run as Administrator.
To back up your files, I'd sort them all into their User folders, then copy those folders to the backup media.
If the Repair Install (upgrade over itself) doesn't work then you can do a Factory Reset here: https://winbuzzer.com/2022/01/01/how-to-reset-w... There's an option there to save your files.
Finally there's the gold standard Clean Install that compiles the best possible Install of Windows which will stay that way as long as you stick with the tools and methods given, has zero reported problems, and is better than any amount of money could buy: http://answers.microsoft.com/en-us/windows/wiki....
To create bootable Windows 10 Installation Media (on another PC if necessary) install Media Creation tool and follow the steps toward the bottom of the download page here in the section "Using the tool to create installation media:"
https://www.microsoft.com/en-US/software-downlo...
Insert media, boot it by powering up PC while pressing the BIOS Boot Menu Key for your PC maker given in this chart: https://www.sysnative.com/forums/hardware-tutor...
If the media won't boot you may need to enter BIOS/UEFI Setup (pressing key given in chart in link above) to turn off Fast Boot or Fast Startup first.
Choose the boot device as a UEFI device if offered, then on second screen choose Install Now, then Custom Install, then at the drive selection screen delete all partitions down to Unallocated Space to get it cleanest, select the Unallocated Space, click Next to let it create and format the needed partitions and start install - this makes it foolproof.
There is a step to rescue your files first using the booted media if you don't have them backed up: http://answers.microsoft.com/en-us/windows/wiki...
You will get and keep the best possible install to the exact extent you stick with the steps, tools and methods in the linked tutorial. It's a great learning experience that will make you the master of your PC because you will learn everything that works best and how to apply it with your own hands.
I hope this helps. Feel free to ask back any questions and let me know how it goes. I will keep working with you until it's resolved.
________________________________________________________
Standard Disclaimer: There are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.