I had this happen about a year ago. OneDrive changed the default path for the Documents folder to the one you mentioned above, but I only noticed it when I wasn't able to find some files in the Documents folder. It turned out that some files were being saved to the default path C:\Users\username\Documents. So I tried to move the Documents folder from the directory made by OneDrive back to the default one, but it gave me an error. Then I tried to fix it in the registry, but there were quite a lot of different entries for the default path, and I wasn't able to figure out which one I should change or remove. In the end, I had to reinstall Windows. Now each time I install Windows on any PC, the first thing I do is remove OneDrive.

Unfortunately, this problem somehow happened again on my current Windows installation. Maybe I forgot to remove OneDrive this time, or it was automatically reinstalled during some update.