How can I create local copies of my files on the Mac Dropbox app?

kvora wrote:

I have selective sync and everything is online. I want to create a local copy.

Did you use Selective Sync, which removes the folder from your local drive entirely (can't even see it in your local Dropbox folder), or did you mark the files as Online-only, so they don't take up any space on your drive but still appear locally?

If you used the Online-only feature, just right-click the file or folder and select Make available offline. Dropbox will re-download the file to your local drive. You can do this for multiple files or folders at a time by selecting multiple files or folders and then right-clicking them.

If you used Selective Sync on a folder, then you would no longer see the folder on your local drive at all. To get a folder back, go into your Selective Sync settings and check the folder(s) that you want to download back to your local drive.

kvora wrote:

I am also considering keeping a synced copy on my Ugreen NAS. How do I do that?

That's out of the scope for what Dropbox does. Dropbox can't copy files to your NAS. You would either have to copy the files manually, or find some other software to do it for you. Some NAS manufacturers have their own app store and some have a sync app that works with Dropbox. I'm not familiar with the Ugreen NAS offerings so you'd have to check with them to see if one was available.

To add onto what Rich said,

Regarding your Ugreen NAS, Dropbox does not support placing the Dropbox folder on a NAS or syncing directly to one. Doing so can lead to sync issues or corrupted files. 

If you want a NAS copy, the safest option is to let Dropbox sync normally to your computer, then use your NAS’s own backup or sync feature to mirror that local folder independent of Dropbox.