Hello, I'm searching for Invoices and wondering if it's possible to get the date from the Item Fulfillment with a join? I've tried some of the ...Fulfilling/Receiving Transaction fields but they don't seem to be working.

There's technically no relationship between the Item Fulfillment and Invoice. Both just link back to the SO. Fulfilling/Transaction will only be populated if you're searching on an SO, Ret Auth, PO or Vendor Ret Auth. As far as I'm aware, the only way to link them is a customization.