A Microsoft file hosting and synchronization service.
Hello,Paul C 195982
Welcome to the Microsoft community!
I have realized that your issue about the two documents.
I wanted to clarify with you that if you set it up to save files locally during the summer. It may indeed be the cause of the problem.
Currently based on your info, a folder is local, are most of the last modified dates the dates you saved locally at that time?
Also OneDrive's folders are still continually kept up to date.
For now, I think you should rename the folders in OneDrive and save them locally, then the files can be merged directly, and you should turn off syncing for now after saving locally to prevent missing files.
But there is a problem, when merging two different local folders, the renamed files are replaced and then the missing files are added together.
But if the data of the renamed files are different, the original data will be replaced.
There is no better way to filter this level of problem. On the one hand, there are too many files and OneDrive does not have the function to compare them; on the other hand, filtering by content is accessing your private information, which is not allowed by Microsoft's user guidelines because it violates the user's right to privacy.
The question at hand is whether your local folder has files that are not currently in OneDrive or that you need to back up. If so you need to filter and categorize them yourself.
Feel free to post back if you need further assistance.
Thank you for your understanding and patience and I look forward to hearing from you.
Ryan - MSFT | Microsoft Community Support Specialist