SharePoint: Designer is discontinued but they haven't released an alternative method of creating custom workflows...
Also, SharePoint only shows correlation ids, which you'd have to check the logs to see what the error was (no description or error code for user): SharePoint Online doesn't split their logs by client... so they can't give clients access to the logs even if they wanted too. Only option is to contact their support... seems overkill when the error may be a user trying to upload a document with the same name.