Best way to backup to external SSD?

I have a 2TB Dropbox account and used around 600GB of it. I'd like to have a backup of everything on an external SSD.

I've read that its highly NOT recommended to install Dropbox on an external drive for various reasons.

So is the only option for me to manually download certain folders to my SSD every now and then? That could be manageable if I were to create a bunch of subfolders (e.g. month's / years) but something more automated would be better