Far as I can tell, you can only link to specific files in Google Drive with the Attachment field type. While I could choose all the files individually, I would much rather just link to the directory because often times we share that directory with a client who will over time continue to add files to it during the lifetime of the project. So only attaching files would become outdated pretty quickly.
Right now I’m just using the URL field type but it’s one more step for me to open drive in another tab and go find the directory and get the share URL. Just slows **bleep** down and isn’t very dynamic.
I’ve seen this functionality in Samepage.io so I imagine it’s in the Google Drive API somewhere. Not to mention from within Gmail, you can attach a directory right there also to an email.