I've made a folder online-only, but it's still taking up several GBs on my Mac computer.

Thanks for posting on our forum, OChannel!

Before looking into this further, I’d just like to mention that adding this character “>” to your folder name isn’t generally recommended, since it can cause syncing issues in some cases (you can read more about this here).

Now, as for the folder size you see on your computer, does your folder contain a lot of files within? The larger size on the disk you see could be because it also includes the files’ metadata. 

Other than that, I’d like to know the syncing status and app version of your Dropbox app, and I’d also like a screenshot of the folder as it shows in your local Dropbox folder (so that I can check its syncing icon).

Finally, regarding your Dropbox cache folder, the Help Center article recommends deleting files from within the folder (if you want to urgently free up space from your computer); it's not suggested to delete the folder itself.

Did you follow these steps and you still can’t see this hidden folder in your root Dropbox? If not, then most likely, you’re using Dropbox for macOS on File Provider (the cache folder won’t be visible in this case).

Let me know what you find.