I finally decided that I wanted to be able to have my entire Dropbox downloaded locally, all the time, instead of using/waiting for Smart Sync. So I bought a Samsung T7 Portable SSD 2TB, Red but it came with a black cable.
Obviously that wasn’t going to work, so I ordered an Amazon Basics Double Braided Nylon USB-C to USB-C 3.1 Gen 2, 1-Foot, Red cable so that I would stop accidentally unplugging the wrong drive.
(You might think that with only two USB-C ports, I would be able to keep track of which was which, but actual experience proved that to be untrue.)
The first thing I did once I had it all downloaded was run Gemini 2 and found about 400 GB of duplicates including, somehow, an entire duplication of my iCloud Photo Library, which was hundreds of thousands of files, not to mention about 100 GB itself.