We're happy to say that users of a 64-bit version of Windows should see their copies of Krita Gemini being updated automatically to the 64-bit version.
The first version of Krita Gemini that was being distributed was only 32-bit in order to help simplify testing and to make sure that it supported a broader spectrum of users before we went live on the store. Some people had reported issues when working with larger files, so hopefully this should make things run a bit smoother!