OneDrive does not like long file names, and to be more precise, it doesn't like long path names. The path is the complete way to get to the file. For example if you have a file called "File" in a folder called "Folder1" which in turn is in a folder called "Folder2" then the path is "Folder2/Folder1/File". This means when you get a warning from OneDrive that it quit because a path was too long, you need to look at the complete set of folders containing the file, starting at the OneDrive folder itself.
Generally you can then rename either the file or any folder in the path to that file which is too long, then restart OneDrive and it should continue - probably finding the next long path, to be honest! (OneDrive is the worst common cloud sync service, in my opinion).
But things can get even worse, because sometimes OneDrive will insist that a path is still too long after it has been shortened, or even if the files or folders have been deleted! This is because there is a second location where this stuff is cached which needs to be fixed as well (shortened or deleted).
Here's how to fix this problem...
Make sure OneDrive isn't running. Note: to quit, click the OneDrive menubar item, click the cog icon, click "Quit OneDrive". In the Finder (Desktop), go to the "Go" menu and choose "Go to Folder...". Type "~/Library/Group Containers/UBF8T346G9.OneDriveStandaloneSuite" and press return. Show invisible files by holding down command and shift and pressing the dot (.) key. Open the OneDrive folder (usually called "OneDrive.noindex" but might have a custom name). Open the OneDrive folder inside this folder (same naming as above, minus ".noindex"). You should see a copy of the folder structure in the real OneDrive folder. Find the file or folder giving the problem and rename it to the same as the real one. Note: the "real one" is the folder you have tried to rename already. Hide invisible files again by holding down command and shift and pressing the dot (.) key. Open OneDrive again. Note: to open OneDrive, find it in the "Applications" folder and double-click it.
You might need to repeat this if multiple long paths are found. In general it is often best to quit OneDrive and correct all the long files before restarting it again... or use a good sync service, like iCloud!
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