Is there a way to view the size of the PDF attachments from within Zotero? I currently have only 11 papers in the group library I just started (my only group library) and it says the group has reached its Zotero file storage quota. I purged files from my library and I can see that the storage for My Library is at 0. I'm not seeing any overly large PDF files when I right click on the PDF from within Zotero and hit "Show File."

If you manually remove a PDF file online from an entry within a group folder, does that remove it from the entry on your desktop? Which way does the data sync from online to the desktop or from the desktop to online? I replaced large files with compressed files in the desktop (right clicked on the PDF within Zotero and clicked "show File"). I want to know if that will replace the PDF online.

Sorry about that. Thanks.

I just tried deleting all the PDFs from the papers in the group folder. I did it from the App because I couldn't see how to delete a PDF out from an entry through the online version. When I synced my group folder from within the app, the PDFs were removed from the online version as well. So far so good. However, even though I have only 11 entries in my group and apparently no PDFs, it still says I am using 299 MB and that my online storage is 100% full. What am I missing?

Regarding your original question about seeing attachment size from with Zotero, the Attachment Scanner plugin allows you to add a column for individual attachment size.
https://github.com/SciImage/zotero-attachment-scanner

Your total online file storage usage is only shown at https://www.zotero.org/settings/storage .