This occurred once before, but then corrected. However, today, I am unable to save newly created Excel 2021 files to Dropbox. I think they are saved, but when I go back to the folder, they are not there.
My workaround is to save to my Desktop and upload the file to Dropbox. I can then open the local copy, edit the file, and save changes with no problems.
I did once receive an error message that said either my path was incorrect, or maybe my file was read-only (it wasn't) or the name had bad characters (it didn't).
These aren't big files, just one or two tab small Excel files.
I have quit Dropbox, rebooted and reopened Dropbox, but the problem persists.