Yeah, it ran through the "upgrading" process and I was able to login and setup sync, everything.
Then when I finally managed to get 6.0.0 running on Ubuntu, it said it couldn't find any data on Google Drive, until I copied down the sync wallet from the Enpass folder (which I'm guessing now is the 5.x data), pointed the first start wizard at it and then relinking to Google Drive after that.