There are a couple of options. If you want to continue using WD Sync then see the following thread, in particular the following post, which details editing a WD Sync file or two that will trigger WD Sync to ignore or exclude certain files or folders. Note that the steps used were on a Windows 7 PC. Unknown if it still works on Windows 10 or can be adapted to work on a Mac.
More than a few have found WD Sync to be extremely problematic and have moved to using third party sync programs like Free File Sync (https://www.freefilesync.org/) for local network syncing. Often third party sync programs may offer more configuration and options than WD Sync. The major downside to third party sync programs is their inability to sync remotely (off site) to a My Cloud using protocols other than FTP which is insecure.
