Currently, in version 3.6.9, the way to do it is using Global Exclusions.

First, Edit Settings:

Then switch to the Other Settings tab, then click Change Global Exclusions:

Replicator will take a moment to check for Network Locations (about 1 minute on my pretty fast PC). This is what eventually was displayed:

These are the Global Exclusions I added (below). I didn't want to backup files that can be downloaded from original sources (which I put in K:\_STATIC_NOBACKUP). I also didn't want to backup derived files like those downloaded or created by the developer tools like Composer, Node Package Manager, Gradle, Nuget, etc:

You'll want to test your new exclusions to be sure they work. Here, I'm checking a Composer directory which is created at the top of this project. All the files and folders in a "vendor" directory are excluded: