Can I include just a folder from Zotero into Overleaf instead of my entire library?
My approach is to select my folder and then manually select the items that I want to export to Overleaf. That might be the entire folder, in which case I can press Ctrl + A to select all items; or it might be most of them. I then select "Export Items" and upload the resulting .bib file to Overleaf.

You can see an example here (selected all but one item I didn't want to cite):