Help syncing an individual folder to an external drive

I'm looking for the best way to keep a specific folder on my Mac backed up to an external drive. The folder is pretty large, a little over 200GB, but it would interfere with my workflow to work directly off of the drive.

I want to routinely copy the contents of this local folder to the drive, but without waiting for files that haven't changed to be recopied. Basically just the way cloud backup would work but with one folder to one drive connected locally. The ability to sync those changes from the drive back to the Mac would be great, but is less important. I don't really need to worry about conflicts because I'll only be using the files in one location at a time.