You're trying to sync a very large file, such as a video or your Outlook PST or OST offline files. For more information, read How to Pause and Resume sync in OneDrive. This can be resolved by pausing and then resuming your sync. Mark the file as ' Always Keep on this device'. You opened an online file and are using Files On-Demand. Select the white or blue OneDrive cloud icon in the taskbar/menu bar to show the list of all files being synced or have recently synced. If OneDrive shows “Processing changes' for a long time, it could be because you have an online file open, lots of files stuck in a queue, or a very large file syncing. Note: After updating to macOS Big Sur, some Mac users may see 'Processing changes' for a long time. No action is required - please wait for the changes to complete.
