I have done a clean install of Catalina 10.15.2 on my mid-2014 MacBook Pro.  An initial scan with Webroot completed in a reasonable time.  I then enabled iCloud Drive.  As I work on both this and an iMac Pro, I selected the option to sync Desktop and Documents folder.  With the laptop having a smaller drive, I selected “optimize Mac storage” to keep older stuff in the cloud.  On the desktop machine, everything has a local copy.  Its initial scan took much longer, but presently everything seems fine and I’ve not even noticed subsequent scans when I’ve been at the machine.

However, with iCloud enabled on the laptop as I’ve said, the subsequent scans have gone on for an exceedingly long time.  When I looked closely, Webroot was scanning items in the Documents folder.  It was very slow, because it appears for all the world that as Webroot wanted to scan each file, iCloud was accommodating by downloading it.  This is certainly not behavior that I want.

At present I have turned off iCloud on the laptop, and am running the scan again.  I would certainly want to be able to exclude Documents from the scan, because I WANT older stuff to stay in the cloud and it has all been scanned on the iMac anyway.  But from what I’m reading, omitting folders is not a thing unless I go to the business product.