I got the same problem. I updated both fee to 6.6 and “Bulk Product Sync with Google Sheets” (this is the new Pro?) to version 6.1. Everything was connected and I got no error when fetching products, but nothing showed up on the sheet.
Problem was in our default setting for sharing sheets -> I had to allow editing of the sheet for everyone who has the link, as this was restricted to “watch only” as default.
I hope this will help someone if they face this issue again.