How do I resolve a selective sync conflict after reinstalling the Dropbox app on macOS?

Hi Nancy, thank you for your prompt reply and clarification, which is helpful, to the extent that it can be. 

I have never consciously chosen selective sync. I didn't actually know what it was until I read about it in one of the threads on here. I do also have a desktop iMac synced to Dropbox but haven't checked that yet. I assume it will have the same problem but I never opted for selective sync on that either. However, when I look in my app prefs on my MacBook I do have folders either checked or with a straight line next to them under the selective sync heading, but I don't know how this has happened.

I did not delete any Dropbox folders when I restored my backup. On the couple of occasions I had to do this before (on my iMac) I had no problem. However, the Dropbox app had not been corrupted on those occasions. I don't know why it was this time, as everything else restored perfectly. I assumed that as the restored folders were older, the online files would sync and update the backup. I don't think this was unreasonable, though I know better now.

I have no grey symbols on any folders. Just the addition of the sync warning to each folder name.

Online, Dropbox says I have no sync problems. 🤷