Desktop & Documents option won't stay checked in iCloud

Hi arla21, before you go the avenue of reinstalling the OS, try some of the following:

So, I just did some searching, what I would suggest is:

1. Reboot your Mac
2. If you're comfortable with Terminal, go in and enter in the following command:

killall bird

What this does is force a restart of the process that syncs iCloud. It should force a new session.

Now go check your iCloud account settings? Is the issue corrected? If not, try the following to see if it is your account at issue or a deeper issue at the iCloud level:

1. Try creating a new user account
2. Log into it
3. Then login into your iCloud account and see if you can have it remain checked for Desktop and Documents. I suggest this as it may very well just be a corrupt preference file causing your issues.

Good luck.

See the article How to reinstall macOS - Apple Support

Files are in original format , make sure you always keep iCloud Drive , desktops and documents box as checked , also apart from it photos , notes , mails ....all the application box must be checked in , erase the hard drive and reinstall Mac OS , the iCloud data in new OS will always sync .

The unknown apps / softwares that are always avoided in Mac won't sync , prefer never use them .