Do you use a backup app? Many backup apps like Carbon Copy Cloner, Resilio Sync and ChronoSync will let you select parts of a drive you want to clone, down to the folder level (and of course on subsequent runs will only copy over changes after the first copy).
Otherwise there are folder-sync apps aplenty, like Good Sync, but the better folder-sync apps cost $30-ish, close to that of a good backup app.
If you’re cheap and are willing to get geeky, look into the rsync command built into macOS - you can even automate it with Automator.
Personally, I’d just create a file-sync process in my backup utility that copies the subset of folders I want to mirror.